as gmun said, they haven't announced all the games yet. they did announce a couple of 'em though, and the biggest relevant ones are SMBA3, the GBA Mario Kart, and Metroid Fusion that i could remember. at the least the GBA ones won't be bad.
free games are gonna be dated accordingly, and to answer 3 as well we get the originals and that's the 'exclusive' portion. there seems to be an implication that some games are getting some extra treatment (unknown to what degree) and you'd be able to get those too. or at least that's the way i read it because otherwise there would be no reason to say that you can get the later ones for free too - if they were the same who cares? if they're different, awesome.
and yeah, just get online, update your 3DS, and you'll get the eshop. easy enough, as is everything online right now (see: one friend code for all).
as for the games, you've a couple options. strange as it may be, Ghost Recon is a good game and plays nothing like older ones. it's an SRPG, you control up to 6 units. it's also on the easy side, there aren't any real unlockables, and the story's entirely forgettable, but the gameplay is pretty good and it's got a pretty decent 3D going for it. there's also multiplayer on it, which is probably a bigger deal, though i haven't tried that yet so i can't tell you anything on that.
the Super Monkey Balls game on it is also good and probably the best entry in the series to date (maybe 2nd behind the original). 3D works well on that game, but you DO have to have your eyes adjust to it more than the others from what i saw.
avoid BlazBlue as it does not have wi-fi play. i also don't really like fighting games on handhelds at all so i can't tell you anything on DoA either, just am a firm believer that fighting games = consoles or PC only. if you don't believe that though, then DoA's gotten plenty of good reviews for it.
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The future must protect the clone's past.
"Maybe it's a tentacle, molesting the planet itself. - Aschen Brodel.