Before I got this game, I had already heard much praise for this game. People were raving mad about it, but it never really piqued my interest. Then it was available in a humble bundle, and I decided to get it and play it.
Holy ♥♥♥♥, is this an enjoyable game. Guacamelee! is a Metroidvania-style Lucha Libre Beat 'em Up with the added mechanic of switching between two worlds. The controls are tight, the fighting feels extremely satisfying, and the game in general feels challenging, but fair. This especially carries over well to the Challenge mode, which are extremely challenging, but allows some margin of error.
There is a fair amount of platforming in the game, particularly when going for the 100%, but it doesn't get in the way. This is primarily thanks to the fact that all special fighting moves that are unlocked in the game are helpful during the platforming segments. This eases up the transitions between the fighting and the platforming.
Furthermore, perfecting the game achievement wise is absolutely doable. It's not easy, but it's not hard either. It's challenging, and can all be earned with a bit of patience and practice.
I finished my first playthrough in about 6 hours, which left out about half of the side quests, most of the collectables, and all of the challenges. Completing all challenges, collecting all remaining orbs and chests, doing the rest of the side quests, and earning all remaining achievements except hardmode ones took me an additional 6 to 7 hours. Completing the game a second time on hard took me 4 hours. And I enjoyed every minute of it.
Some people might be less enthused about hardmode being locked until you finish the game on normal, but there's a workaround for that, as can be found here: http://steamcommunity.com/sharedfiles/filedetails/?id=168142136
The soundtrack on this game is excellent as well, which I have now added to my usual playlist.
One final thing though: screw those skeletons in the yellow ponchos. Bloody annoying buggers.