Big eShop fan here, so I'll weigh in for sure. Wii U may have seen sparse major releases at times, but with all the gems on the eShop I've played more games on it than any other platform. Also really, really helps that many of these went on sale for absolutely dirt-cheap.
Favourite Wii U eShop games:
Severed - Loved this hack & slash game from start to end, perfect length, affecting story too.
Sky Force Anniversary - Tremendous shoot-em-up. Simple, but so, so addictive.
Affordable Space Adventures - Probably still the game that best used the Gamepad, absolute must-play.
The Swapper - Creative puzzler with an interesting story, fantastic production values on this one.
SteamWorld Heist - Clever turn-based strategy game with good replay value, very few complaints here.
Jotun (Valhalla edition) - Darn tough action game, nice hand-drawn art look, cool tough bossfights.
Shantae & the Pirate's Curse - Really good Castlevania-esque platformer, don't like the cheesecakey art.
Nano Assault Neo - Very stylish shoot-em-up, bossfights are letdowns though.
Tengami - Very calming adventure game presented in origami art style & soothing David Wise tunes.
Star Fox Guard - Creative use of the Gamepad, I suppose this got a print run but pretty limited so it counts?
Art of Balance - Takes a while to get to the good puzzles, but this is a relaxing timekiller.
Octodad: Dadliest Catch - Very humorous game with outrageous controls. Best in short doses & multiplayer.
Mid-range titles I would cautiously recommend:
Never Alone (Kisima Innitchuna) - Buggy platforming overshadows this atmospheric educational game, sadly.
Nova-111 - Mixing realtime & turnbased elements is a great idea, but this way overstays its welcome.
Nihilumbra - Nothing really wrong here, but it's a fairly simplistic puzzle-platformer with heavyhanded story.
Little Inferno - Mildly humorous game that doesn't quite land its meta message, in my opinion.
Gunman Clive Collection - These are pretty difficult cowboy Mega Man games, great art, bit stiff controls.
Blek - The handwriting aspect of this puzzler is a great idea, but man did it make me feel dumb.
Back to Bed - Solid puzzler, but a bit too short and unvaried to recommend at full price.
Bit.Trip Runner2 - This is a really good game, but honestly also pretty frustrating. Mileage may vary.
Edge - Finnicky controls and trial & error nature make this pretty frustrating. Catchy beats though.
Forma.8 - Tremendous worldbuilding, but just a tad too complex & dense, making it a bit inaccessible.
Spy Chameleon - Fun gameplay idea here to switch colours to stay hidden. More story effort would've helped.
SteamWorld Dig - In my opinion this one takes too long to get going, ending is great though.
Stealth Inc. 2 - The overworld is more of a hindrance than an addition in this trial & error puzzle platformer.
Whispering Willows - Honestly a pretty flawed adventure game, but I enjoy these low-tension games.
X-Type+ - Addictive score attack shoot-em-up. A previous version is on the devs website, for free.
Year Walk - Relatively unsettling/scary adventure game. Horror is an underserved genre on the eShop.
Disappointing titles:
Midnight 2 - I like the golf-puzzle idea and presentation here, but controls aren't quite there yet.
Mini Mario & Friends: Amiibo Challenge - If you don't have Amiibos there's about an hour of okay~ish Mario & DK style puzzles here. Free though!
Still interested in these:
Axiom Verge - I've ordered the physical version for this, love the idea of a 2-screen Metroid style game.
Ghost Blade HD - This Dreamcast homebrew game looks like a cool shoot-em-up. Gonna get it soon.
FAST Racing Neo - Love F-Zero, but I've read the A.I. in this are rubberbanding cheaters?
Earthlock: Festival of Magic - Kinda wanna try this RPG, but I'm not really sold yet.
Völgarr the Viking - Looks cool, but apparantly it's absurdly difficult - and I don't have great reflexes so...
The Fall - This is one I don't know a lot about really. Used to get this and the Swapper mixed up, they look so similar in screenshots.