There are two trends in game design/mechanics/genres that are really bugging the heck out of me right now: deck building card games, mostly clones of Dominion with a new theme and mild mechanic changes, and tower defense video games, which just copy each other and flood the iTunes app store.

Deck Building

 To start with, I have some issues with the genre/mechanic.

1. If you're not really paying attention, it's very easy to make mistakes early on in the game, and incredibly difficult to undo those mistakes in any kind of optimal fashion that allows you to compete with the people who didn't make mistakes.
2. Depending on the game and the cards used to play it, there's also a lack of player interactivity. You're almost kind of playing solitaire and there's little you can do during someone else's turn to hinder or influence them.
3. Lastly, there tends to be an optimal strategy for winning each game, with all other strategies being sub-optimal and less attractive, so games kind of end up being races between those who know the "solution" to the current configuration of cards, and utter failure by those who realize too late what the best plays should have been.

Granted, I've only really played Dominion, but I've read up on the rules of most of the others that it's very easy to say "seen one, you've seen 'em all."  The exception to this might be Puzzle Strike.  I haven't read the rules in detail, but game designer Sirlin broke down the differences adequately enough to convince me it's a different, and improved, evolution of the genre.

There are some neat ideas in the deck building genre, some neat design mechanics (if the game doesn't play the way you like it, swap out the cards you don't like and put in others that interact in more interesting ways), and I'm not totally opposed to playing these games, despite my complaints above.  I think my biggest issue is that everybody seems to be making games in this genre!  The mechanics change little, if at all, from the original Dominion template, and all they do is slap on this or that property and call it a day. (Resident Evil, Star Trek, and the recently announced Penny Arcade deck building game are all examples)

Perhaps I shouldn't be complaining, as it's not like we haven't seen this before, and I probably need to give the genre time to diversify.  Magic: The Gathering created a whole new gaming industry when it became the first collectible card game, and there have been some worthy and interesting evolutions, and plenty of tasteless, tacky "quick buck" clones.  For the time being though, I'll just keep rolling my eyes until I see something really different and enjoyable.

Tower Defense

Ugh, I hate this genre, and I hate how prolific and popular these types of games are.

I understand the attraction, it's very fun at the beginning and it's a neat combination of strategy and base-building/city planning or something.  But I very quickly reach an event horizon with these games, where the number of enemies you have to defend against just becomes insurmountable, and the strategy stagnates, boiling down to "I have no more room to build stuff, nor any reason to change the layout of what I have, so I'll just keep upgrading my units."  And again, there are *so* many clones out there that do little to evolve and refine the basic idea, and just slap a new theme on the same old thing.

Atomic Zombie Smasher is my exception to the rule, thanks to a few design decisions.

Each city has as different layout, and you always end up with a different set of units available for you to use to defend with.  The units all behave differently in both attack patterns and placement restrictions or mobility, so they each require different tactics, which also change depending on what other units you have at your disposal.  You're also always "starting over" in each city, so you never end up stagnating, getting stuck in the defense structures you created.  Lastly, the game isn't so much about defending and killing - there are often too many zombies for you to accomplish this - but holding them off long enough for you to get your helicopter in and pick up as many humans as you can before the city is overrun.

It's definitely a kind of tower defense game, but because of these changes (and it's really kitschy design style) it never suffers, IMHO, from the problems I outlined above.

I think there's hope for Deck Building games. I think there's enough interesting stuff going on there and the basic idea has a lot of potential to give rise to some really great games, but I just don't enjoy Tower Defense games, and don't think I ever will. :P