New Super Mario Bros. U: I haven't played any of the other games barring a brief political stint with NSMBW at DLCon, so...yeah, keep that in mind for some of my comments! Actually, this is going to be a brief rant.
That said, finished the main game. Outside of a few levels near the end, the game is a tad too easy; Only a few stages I actually died, even less I died multiple times (though these stages I died 5+ times because Luigi box appeared), and the game hands out free lives like candy. I had over 80 lives by the end of the game!
Still fun if easy at times. The boss variety is neat too, albeit fighting that SMB3 Mini Boss a bunch of times got old. They did try to make him different in a number of ways, but still felt like the same fight over and over again. The Koopalings being in the game is always a treat, and the fights were creative. Roy and Ludwig stood out as the most interesting fights to me, albeit most were still easy (none of them had me dying more than once.)
The last Mid-Castle having Kamek as the boss was a nice touch, though, and he's a legitimately fun fight. Nice change of pace from fighting the same guy 6 times, and it always bugged me in Yoshi's Island that you never actually fought Kamek seeing as he was the game's main villain (albeit, to Yoshi's Island's credit, the Baby Bowser twist at the end was funny. Kamek just being the stooge for a whiny, toddler whose entire motive is "Wants to ride the weird green pony" was just glorious and fits into Yoshi's Islands less-than-serious narrative well.)
Bowser Jr...needs to go away. He's so forced into this game it can't be emphasized. He pops up mid-game, does that laugh which gets old REALLY FAST. There's a trademark, and then there's being a one note pony who can't do anything else. All he does is appear, "AHAHAHAH!" then try to act like he's awesome. Go away, you're not amusing, you're annoying in that cute way, and you completely fail as a villain in any sense, and every scene your in is a scene they could have put Bowser. His first boss fight is the over done "hit target with their own heat seeking missile" gimmick that I've seen in Mario Galaxy multiple times already, and it's even less interesting here because 2D. Swim around in a circle, slight sharp angle, success. ALso, shoving his face in a bunch of castles near the end adds nothing to the game in any sense. It's just "that is ugly, and not in a good way." Bowser Jr., you are NOW Bowser, and you never will be.
The 2nd fight tried, I guess, but still came off as forced. Didn't help that it was tied to probably the most annoying stage in the game; the only self-moving stage, which I can deal with, that also forces a Motion Control gimmick that the game never eevn touched upon before. No, seriously; the game never really touches Motion Controls until this point, then goes "Oh yeah, start tilting the Wii U Gamepad to move this thing." Wish they just did, I dunno, balance based controls, as in, the platform moves based on where Mario is standing; I know they've done this before, but it feels more natural than the pad.
Bowser himself...well, I do love the whole retro thing leading up to him, and the retro style fight itself! Of course it's a blatant cocktease because it's too simple and the final boss fight is probably the one time they actually made use of Bowser Jr. in a remotely worthwhile way.
Oh, and Ghost Houses are annoying. Part of this is the music; it's annoying after the 2nd loop. The other problem is the gimmick of "illusion based stage" gets old. Yes, I know Super Mario World had them, but I remember there being less of them and they were better spaced out. I'll give props to the final Ghost House though; the rotating rooms was a neat gimmick.
Anyway, was decent fun, but won't go WOMG AMAZING or anything. The Multiplayer still exists of course and that's as trainwreck and friendship breaking inducing as always...especially with a 5th player. I played Single Player because I knew Multi-player would never allow me to actually finish the game <_<