Terrible script and acting wasn't great by most of the cast (Ian, Patrick and Hugh were the best), terrible action scenes (they constantly got their asses handed to them by mutants weaker than them and then had one moment of win), Cyclops was just a whimpy boy scout, nothing alpha about him at all (this applies to all the films that he was in) and in general just little things that annoyed me. It started of good but just got worse and worse imo.
Whilst Stryker was the weakest villain i.e. no mutant powers, he was very deadly due to having military control and experience, mutant son and mutant sidekick etc. i.e. just look at how far he came to succeeding in wiping every mutant out in the world, the x-men even had to team up with Magneto etc. in order to stop him and his plan.
For me, x men first class is better than all of those 3. Whilst it might not follow the comics or cartoons (have seen every episode of the tv series) as closely, it makes for a better "film" imho.