GW2 has very nice graphics, a big world, a good dye system, jumping puzzles are fun, fluid combat and it is good there are no macros/plugins, but that is about it, oh the interface is very good in some respects such as the depositing resources, but then in others liek lack of customization, not so good.
But does it ruin other MMOs, no not really, if I’ve been playing one game for a while then try another it always takes time to adjust, but after a while I get used to that new game. GW2 is nothing special, other than the benefits of being newer (nicer graphics) and being in the minority of MMOs with an action type combat system, it is really just more of the same old thing, EVE Online is far more innovative / different from other MMOs than GW2 is.
Then of course there are the bad parts about it, the game was shipped half finished, especially in areas like sPvP, I have never played an MMO where bugs take so long to fix (they seem underresourced), WvW turned out pretty meh and bascially DAoC did it better years ago (and I expect many of those left are simply only sticking around until the release of…), sPvP outside of the nice fluid combat and gear normalization is simply bad (as what is left of the population shows) and PvE is super casual and somewhat zergy/spammy, which I guess is fine if you like that sort of thing, but as someone who is not a huge fan of PvE fullstop the only thing that kept me awake was playing a class that required lots of multitasking / awareness in a raid. (No I am not refering to WoW, never played it, never will, having all those addons play the game for me looks very dull indeed)