Pokemon Black 2: Completed, main game anyway. Aftergame...let's just say I am throwing any sense of being fair out the window, and thus have shoved in two ubers that aren't in UNova in my team!
Final Team was Samurott, Umbreon, Lucario, Thundurus-T, Haxorus, Arcanine. Samurott was token water type, you basically always want one of those, Umbreon was really damned effective at tanking, feeling basically immortal, and Snarl made him excellent for crippling any specal reliant folks to allow Haxorus to swap in and set up on. Also gave him Toxic, because he's actually durable enough to make use of it. Haxorus, speaking of, existed mostly for Dragon Dance x2 -> Things die. Getting the turns to do that was sometimes tricky, but even when he couldn't, that's still 147 STAB Dragon Claw. Lucario was just good for multi-purpose damage hitting, and had Sword Dance though in hindsight he's not quite fast enough to make full use of it. Arcanine had Intimidate and will-o-wisp, thus completely maimed anything relying on Physicals, also had Flare Blitz for a big damage STAB, Wild Charge for type covering, and Outrage for something that didn't kill him; Shell Bell used to mitigate recoil some. Thundurus...fast, hits hard with electric attacks, the usual stuff. Also had T-Wave and Swagger for some status, and Fly because...uhh...convenience or something.
This is easily one of, if not the best, Pokemon game based off the main game thus far. The only flaw is that it's a little easy for bosses, but the average trainer is harder I find due to them generally being higher leveled than usual, and since there's so many Pokemon, the variety of things trainers use is interesting and hard to predict. Additionally, existence of Challenge Mode in Black 2 probably helps mitigate the difficulty thing, though pity you have to beat the game first, or at least find someone with a completed save to unlock it from the outset (which can be transferred to White 2 as well, for those who got that version...god knows why White 2 has an easy mode unlocked AFTER COMPLETING THE GAME, doesn't that defeat the purpose of Easy mode?). Worth noting that the E4 all use only 4 Pokemon instead of the usual 5, and gain an extra in Challenge Mode, which I found odd; champ was about what you'd expect for a Pokemon final boss.
Ok, a second flaw is that there's a GOD DAMNED SEWER DUNGEON. IN A POKEMON GAME! I don't have to say anything more; "Sewer Dungeon" should say everything about why that's a bad thing!
Otherwise, it is the most polished game in the series, taking everything BW1 had, and adding a few other small little features in further, as well as upping the actual options a lot by putting in a bunch of earlier gen Pokemon, and the options are rather interesting to boot (like, say, Riolu ridiculously early for example)...yet there's still no Abra or Geodude which is disappointing given their previous stapleness...ah well, either way, lot's of interesting options nonetheless.
Also, GAME HAS PLOT! BACKSTORY! ATTEMPT AT CHARACTERIZATION! Whether it does a good job with this or not is a different story, but at least it shows genuine forward effort in this regard! I know someone is going to trash the game for trying to have things like that in a Pokemon game and failing, but frankly, the game isn't deep enough to be offensive, so even subpar at everything listed above I'd say is superior to what the series offered before that...
...then again, I am now reminded of EXPAND THE LANDMASS! and...well...the entirety of Team Galactic, so maybe I have to reconsider...
I would say "skip BW1, just go for the sequels" if you haven't played Gen 5 yet, except the sequels act like you've played the previous game in terms of plot and make a bunch of nods to it (and BW1 is a good game in it's own right!), and POKEMON PLOT!!! is totally srs bsns and important stuff amirite?