Granted I have had my Wii U since 2013 but in an overall perspective it hasn't done much of a progress at all because in terms of being a quality gaming console it isn't, nor does it have a whole lot to play and then there's the GamePad which should have never been forced upon the Wii U - which is a home console after all. The online services feel very primitive and limited lacking features such as voice chat then you have the menus such as System Settings that take up to 30secs to load plus Miiverse to open lasts for about the same as System Settings. Then there's the Wii U Pro Controller which is despised by Nintendo as Nintendo itself doesn't support the controller on its games sadly, but I love to use it as it's light-weight, 80hrs of use and very comfortable. I'll say that I have played over 50 Wii U games but just don't do it, if you'd ever get one just get Nintendo games and call it a day. Heck, even Nintendo exclusives on the Wii U aren't all that good, i.e, Hyrule Warriors, Nintendoland, Game & Wario, Kirby and the Rainbow Curse, Mario Party 10, ZombiU, Wii Party U, New Super Luigi U, New Super Mario Bros. U and Sonic Boom. I think this is all of them and wow, it's 10 in total. Nintendo's losing their own sense of "Seal of Quality" but they have been on a quality decline ever since the N64 so no surprise there.
The Wii U still has several months to go before it's 3 years old. That being said I haven't purchased a Wii U and don't plan on it until Xenoblade Chronicles X comes out, that alone is basically enough for me to purchase a Wii U. Granted there are other games i'd like to play that are on the Wii U but those are to a lesser extent. On a quality decline since the N64? The NGC has a pretty good run up of exclusives and even more so with the Wii, which sold like hot cakes. Also, these are all the Wii U exclusives that I would consider to be worth picking one up for: Bayonetta 2, Captain Toad: Treasure Tracker, Donkey Kong Country: Tropical Freeze, Fatal Frame: Oracle of the Sodden Raven (TBA 2015), Game & Wario, Hyrule Warriors, Kirby and the Rainbow Curse, TLoZ Wind Waker, TLoZ (TBA 2016 unfortunately), Mario Kart 8, Mario Party 10 (unless they're just like the previous ones, those weren't really worth it), New Super Luigi U, New Super Mario Bros, Nintendo Land, Pikmin 3, Shin Megami Tensei x Fire Emblem (TBA 2015), Star Fox (TBA 2015), Super Mario 3D World, Xenoblade Chronicles X, Zombii U, Super Smash Bros Wii U (I still consider it exclusive as the 3DS is pretty weak in comparison.), Yoshi's Woolly World (TBA 2015). Even then, that line up still is a little weak considering that the Wii U has been out since November 2012 but they're fairly good game or for the TBA ones, they look like they'll be really good.
In an overall estimate it's 3 years as 2012-2015 it's 3, so that's the whole point. A good chunk of the games you listed aren't even out and Game & Wario, seriously? If you're gonna get that then grab Nintendoland instead. Tropical Freeze is such a boring and bland platformer and the music doesn't help it either as not a single one is memorable, despite that it's praised by many I don't really like the game. I bought it due to the exceedingly positive feedback it had, unfortunately. Mario Party 10? Oh I'm not even gonna go there.
It may be an overall estimate but it's grossly inaccurate. The Wii U isn't even 2 years and 6 months yet (almost there but not quite). That's like saying it's 3 years old if the console came out December 31st of 2012 and January 1st of 2015 rolls around and it gets that whole year simply because of the year and not the month or day. The Wii U's weak exclusive line up isn't really any different than any other console that's out. Granted, they haven't been out as long, when I see top 12 lists for games, usually 4-5 are exclusive to that console and then the rest are multi-plat. Unfortunately a lot of developers are afraid to make a Wii U exclusive game because the somewhat poor sales of the Wii U, granted, I'm rather sure they've exceeded 4 million, which is quite a bit, it's still not saying much to PS4's over 10 million. Anymore a lot of consoles just seem to try and pump out the biggest AAA title that will go to all consoles to generate a large profit because if they don't, they seem to end up going out of business.
I have to say that I must agree with the OP. Not much games are released for the wii u and I think it's just dying a slow and (not so) painful death. I hope the new console Nintendo has announced (=rumoured) will do better. Upcoming Wii U Games: Release Dates - IGN Not much to look at...
At this moment in time I think all the current gen consoles don't really have a strong line-up, however we do need to remember that the last console generation lasted over 8 years before all the current gen consoles were released, each console had a lot of time to build up a quality library of games. The first couple of years after the Xbox 360's was released the line-up was pretty weak, I enjoyed the arcade games a lot more than many of the retail games out at the time. If I owned a Wii U right now I think i'd really enjoy: Bayonetta 2, Donkey Kong Country: Tropical Freeze, Mario Kart 8, New Super Mario Bro and Super Smash Bros Wii U, which for a console that's been out for two and a half yes is not bad, it already has many of the major exclusive franchises i'd actually want to play. I also think it depends how much time you have to actually play on the console, to decide if the console is currently worth it. I've worked full time for a couple of years now and am no longer a student, so find I hardly play games now compared to how I did a few years ago. So the above games I mentioned would be more than enough for me. I have a 3DS and own 3x games on it, yet to me I think that's been a totally worth while investment, simply for the amount of time I've enjoyed playing those 3x games on the console.