There's always a right way to play and a wrong way to play. If you're a beam/tac arrow blaster and facetank things in melee, you're doing it wrong.
If you're a defender and didn't slot any of your primary powers on a set like poison, dark or cold, you're doing it wrong.
If you're a fire armor character and skipped burn, you're doing it wrong.
If you're a sentinel, you're doing it wrong. (:>)
As for gimmicks: I don't personally mind gimmicks, but when you add a gimmick to an existing set, it has to be consistent. I actually don't mind energy's new gimmick on scrappers/stalkers, largely due to their ability to reliably get crits. I however, don't like how brutes don't get the chance to obtain two focus stacks per rotation. That objectively makes those versions better no matter how many reds the brute or tank eats. Having that extra ET per TF cycle is massive. Why would I ever use power crash on a brute?
Other times, the gimmick flops. The two most notable examples of this are Dual Blades, and the new Seismic blast set. Where the mechanics are so inefficient that you're better off ignoring both. Dual blades could stand to be more dynamic with how combos work, in addition to some attacks being sped up. Seismic should have more empowered abilities, or rock shards/stalag should be made into something that isn't a total meme.
And in some cases, the mechanic is implemented very well. Paragon did great with Gravity and Street Justice(2cp builder for non-stalkers would be nice though), the new Elec Blast rework by HC is almost flawless (buff tesla cage), and Bio is set all about gimmicks, and there's very few people complaining there. Some crying for nerfs, but if they think that'll magically bring balance to the game, ha.