How long are you gaming?
You know we had lots of those on PC once upon a time.

Not a platformer. Also well worth the time put into it. It's pretty funny and is a really likable beat-em-up.

As for the platformers, it's like any other genre. If you like em, you like em. Why should you buy the next FPS-alike? Because you like shooters.

As far as Rayman goes, it's incredibly charming and the levels are well-built on top of having really good art. Also, it's got up to 4-player multiplayer in the recent entries.

Spelunky is part roguelike and it's got a really well-balanced level of challenge. Rogue Legacy is also part roguelike though I haven't played it so I couldn't speak on its merit.

Humm. Not sure if I misread your post, but platformers have already been a staple of each and every even remotely successful platform, including the PC. There is a long string of hundreds of popular PC platformers from the 80s until now, including such iconic games as "Duke Nukem" (and other Apogee games), "James Pond 2", "Abuse", to Indies like Braid, Trine, etc.

Granted, there have been several exceptionally good platformers coming out lately (Giana Sisters for example), but what exactly is your question?

The best way to find out is by playing them! That way you'll also learn the difference between jump 'n' runs and beat 'em ups. ;)

Well, I started gaming in the 90s, like good old isometric strategy games and RPGs, but these platformers look and feel like really old kiddie jumping games. Is it about retro?

Good platformers are really fun; if you never play them because you think they're "kiddie" then you're missing out. It's your decision, though.

I rather have that than all the super-serious-warface-brofist BS that's been so prominent in action games lately.

I definitely enjoy that there has been a bit of a resurgence of jump'n'runs of late, which I've been playing since the '80s, starting on the beloved breadbox (aka C64).

No, platformers have never gone out of fashion.

It's not only "jumping". Platformers are very diverse and employ lots of extremely different gameplay mechanics. "Braid" has lots of clever puzzles which deal with the concept of time. "Trine" has physics-based puzzles and RPG elements. La-Mulana is a staggeringly huge open world with a complex background story (and in which your character learns many new skills over time). "Giana Sisters" is an amazingly detailed take on the "two parallel worlds" concept, with quite challenging gameplay. "Limbo" is one of the most atmospheric games I played lately.

As with any other genre, there are platformers which qualify as the "kiddie stuff" you seem to have in mind, and platformers which combine engaging gameplay, innovative ideas, and parts which challenge your mind instead of your reflexes. Just look around with open eyes, they are easy to spot.

Why must 'kiddie' always be used as a derogatory term?
Sometimes I'm in the mood for a simple, happy and fun game.
Probably more often than I'm in the mood for those depressing grey and brown 'realistic' games that are so popular.

They are easy to get into and something about the simplicity of 2D, even better with RPG elements.

Because true art is angsty. :P No, but seriously, people proclaiming something that's colorful or happy is "kiddie" is a personal pet peeve of mine.

*Warning: The above is a TvTropes link.

I grew up on the old NES and never really like platformers myself so part of me can see where you are coming from, however if you have the time and a few pennies you might want to try some of them. Some of them might surprise you, they sure did me.

That and what Nirth said.

They were on you beloved pc long before they made their recent comeback with newer versions like giana sisters and so on.

The PC had a good number of platforming games in the past, such classics like Duke Nukum (It was spelled like that for a while...) and Duke Nukem II, Jazz Jackrabbit, Jill of the Jungle, and we can't forget the classic and pretty important milestone in PC gaming, Commander Keen.

I guess the reason why they are so fascinating is the retro thing, but for most of them they are interesting because they are easy to pick up and play, and for some like Spelunky, take some practice to master.