Why the Archon 'failed' as an enemy.

I'm talking from your perspective as a player.  When you first see them Miranda tells you what they are, and what they have been doing, and you're left to wonder why they are now working for the Reapers.  You don't find out the truth until later on.  But they aren't portrayed as being evil for the sake of being evil.  They were already bad people from your perspective.

It's because the Kett were the only main villain.  In ME:1 you had Saren working on behalf of the reapers using Geth, so that the reapers could remain in the shadows and keep their air of invincibility.  Then when Sovereign finally comes out he lays waste to the citadel fleet and defense so that now you're like if one can do this, what can hundreds do.

In ME:2 the collectors had limited missions, and you spent most of the game killing mercs as the fodder enemies.  When you did fight collectors you snuck onto their ship and then escaped, you didn't constantly overrun them and defeat them.  They killed you in the opening scene and kept you in fear thinking that you needed to improve yourself and your capabilities to fight them toe to toe again, which happened at the end.

ME:3 the reapers actually came and they spent the whole game beating you over the head with the idea that you couldn't beat them conventionally.

Now ME:A  Kett are main villain and the fodder enemy.  You're defeating them soundly from the start, the prologue.  You take the vault from them on Habitat 7, you take a base and their exaltation facility on Voeld, you overrun the Archon's flagship, and then take back the Salarian Ark, take back the Asari Ark.  The exiles run them off of Voeld and put their heads up on spikes as trophies.  Where were they ever cast as formidable up until the very end of the game?  They never built them up.

Even though Saren was a surrogate, he still stayed a step ahead of you and succeeded in what he was trying to do on multiple occasions.  Kett had no victories, offered you no setbacks.

Think of the end of ME2 when you see the sea of reapers, you're like oh crap.  Now in ME:A when I see the new Kett leader turn and walk away from the window, I'm like, who cares.  I'm not scared of them. 

The Archon left me totally indifferent... which is a very bad point.
I like to love or hate a villain. Indifference is the worse thing that can happen.

I picked success simply because of how evil he looks and acts. Is he one dimensional? Yeah but most antagonists are at least in games and movies. Books it's easier to write the motivations and such than it is here.

The Archon was not a good villain, it was not a bad villain either...it was simply meh which is actually the worst thing you could be. The big issue of BW villains is that you interact very little with them, you don't see what kind of person they are, what they stand for, what ideals motivate them to do their actions. Villains need to be relatable, you need to empathize with them to some extent. I liked Loghain, Saren and TIM (pre-ME3). They were very interesting and charming personalities you always wanted to hear.

OP your comparison of BW villains with Gaunter O'Dimm is simply unfair, he is the devil himself you can't beat that.

An antagonist is only as strong as the threat he presents, and the enemies in MET were at least credible. Their technological capabilities, their military doctrines and their motivations all stacked up, the Kett are a mess in that respect.   

Whenever we see Cerberus, the Collectors or Geth in action they are always acting with purpose, carrying out a mission, usually with a high level of efficiency and brutal maleficence until the hero shows up and throws a spanner in the works.  The vast majority of Kett we see in ME:A don't seem to be doing anything, they are just standing around waiting to be shot at, yet we are supposed to believe that they are a highly ordered, disciplined military force acting with unified purpose.... They fair no better off camera...

This, is perhaps the Archons greatest failing, he has noting to back up his bravado, his forces are a joke who literally die in their thousands to a 20-something with next to no military training!  The Geth, the Collectors, the Reapers, even Cerberus, were credible on and off camera, dangerous, terrifying and well capable of inflicting grave harm.  Not to mention that Saren, Benezia, Sovereign and Harbinger were all dangerous in their own right, the latter two capable of rending whole fleets of war ships to scrap.   Archon has next to nothing going for him in terms of being a strong antagonist. 

I certainly didn't think Cerberus had clear motivations or even credible technological capabilities relative to their stated origins. In fact they seemed to be able to do whatever the plot required of them at any given moment whether that made sense or not. And I'm sorry but Benezia and Harbinger were no where near as developed as Saren or Sovereign. We must have played a different OT.

Yeah that's why I picked success too because he very nearly does beat us on quite a few occasions as well. Let's not forget that Ryder does technically have to commit suicide by letting SAM kill them to escape the Archon's trap and then again when the Archon takes control of SAM and renders what he thinks the pathfinder helpless which in truth he nearly does. At the end of the day I feel the reason why we do manage to win in the end is because the Archon underestimated Ryder's drive and resourcefulness to beat him. Also had the Kett ran with the Moshae and not decided to hang around to try to hold Ryder off Ryder would never be able to rescue her during that quest.

It has a lack of malice atm because it is unknowable. But it is by the look of it a self-procreating construct build by someone to expand to the areas of the cosmos where the live organisms cannot travel, come on the site, and build a habitat and an organic race from a genetic blueprint from scratch. It is obvious that someone (not unlike Shepard who blew up the harvesting and reseeding cycle set up to preserve the lifecycle in the galaxy) did not think that this creation mechanism is a Good Thing, so Scourge was created to devour their installations & mess up their project. All their installations are resisting tempering/penetration by either Ryder or Kett, and the ancient Angara AI was not a friendly piece of code either. We also do not know if the Remtch is not unlike the Ring in the LOTR, it grants powers to the user, but it only serves one master, and who that master is... unknowable.

In lieu of having a well-written, believable character, a villain should at least be fun to hate. The Archon certainly failed in that regard, IMO.

So did what's-his-face in DA:I. I just never cared about either villain at all.

I think we have a bit of a miscommunication, when I say credible I mean credible as an antagonist, you can imagine that without your intervention they would be succeeding at what they are doing.   Their appearance always has a purpose and they are outfitted appropriately to fulfil that purpose.  Examples being the slaughter on Mars (android infiltrator), the assault on the Salarian R&D base (jump packs and shuttles), the rounding up of civilians at Gateway(stun batons).  I'm never left thinking, why are you here?  How did you expect to win?  What are your goals?  I'm not going to pretend that I don't have any problems with Lazarus, the construction of the N2 or TIM's overarching plans, but Cerberus, like the Geth and Collectors, while fulfilling the same role at the Kett 'Cannon Fodder'  appear in the game as a credible fighting force with purpose that you can believe are a threat... the Kett no so much.  

 And I have no idea what your second point is referencing, is it from someone elses post? 

Really? Cerberus is credible to you? Okay. What are Cerberus' motivations then? How did attacking Sur'Kesh advance their goals? Or staging the coup on the Citadel? Where are they getting all their foot soldiers and advanced weaponry that rival the forces of the entire intergalactic defense force? If you're gonna handwave that away with "reaper tech" then why doesn't anyone else have the capability to process this reaper tech into infinite war assets?