Although it's the only musical instrument I've ever had any working knowledge of, I've never sought out any of the various piano arrangement albums for video game music, save one: the Brandish Piano Collection, which I obtained years before I even had any idea who/what Falcom, JDK Band and the Brandish series were....and certainly before I came to greatly appreciate the music of the series. The arrangement of "Begging's One Life" (the game over theme for Brandish 1 and 2) is a definite favorite of mine. In fact, here:

Begging One's Life (Brandish 2 SFC version)
Game Over (Piano Collection version)

Anyway, I could've sworn there was a "best piano album" topic around here somewhere, but since a search doesn't turn it up, I'm guessing I hallucinated it. So...

What are the best piano albums based on video game music? What are the worst? Is there anything worth going outside my comfort zone (mainstream gaming) for, like erogame piano albums?

Any and all opinions welcome (at least for now).

The only piano album I can really recommend is Piano Collections FFX. Hamauzu's arrangements make the album shine, as opposed to being a same-song-just-on-piano arrangement. Unless that's what you're looking for, in which case I'd recommend almost every other piano CD out there.

Ever tried listening to Final Fantasy VI and VIII Piano Collections?If you played the games and liked them,these soundtracks should be listened to,just to check...I wouldn't recommend FF V Piano Collections,though,and wasn't much impressed by the ones from FF IV,VII,IX and X-2.For FF X PC,I definitely agree with Zane.Some other things to check,that I haven't listened to "carefully" yet: Dragon Quest VII on Piano,and SaGa Frontier II Piano Pieces.I've never listened to the different Suikoden Piano ones,so I won't say anything about them.

Totally agree with Dais on Brandish Piano Collections, what an awesome album that is! Beats any other Falcom piano effort.

Also recommended are the Elf Music World albums, especially the first.

Hamauzu on piano is always lovely, wish he would make another Saga Frontier 2.

I am a self-proclaimed expert on this topic. Here we go:

AMAZINGLY GOOD VGM PIANO COLLECTIONS
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Brandish (as Dais pointed out)
SaGa Frontier 2 (as Thomas pointed out)
Final Fantasy X (as Zane pointed out)
Final Fantasy X-2 (only if you like jazz!)

Kinda-sorta good ones
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Arc the Lad Piano Album
Sailing to the World Piano Score (Mitsuda composed, Hamauzu arranged = guaranteed decency)
Final Fantasy VIII Piano Collection
Final Fantasy IX Piano Collection
Sega PIANO Nocturne

Not really worth it, but some people might like them
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Legend of Heroes Piano Collection
Ys Piano Collection
Ys Piano Collection 2
Virtually everything else listed at RPGFan.com

Generally awful
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ANY Dragon Quest Piano Collection. They're made for children. Like, four-year-olds. SO bad. VII is okay, but anything before VII is just crap.
Final Fantasy V Piano Collection -- easily the worst of the bunch.

That's the word on the street. You want the top-notch stuff, it's gotta be SF2, FFX, and Brandish.

SaGa Frontier 2 and FFX Piano Collection are the only ones I can fully recommend. Granted, there's several I haven't heard yet (like Brandish). Most of the time, you just get boring simplistic chord/melody arranges, not even remotely taking advantage of the instrument.

Most VGM piano albums are extremely dull, but the Brandish and Arc the Lad ones are worth tracking down.

Arc the Lad is bombastic, which is fun, much like the louder tracks on FFIX Piano. But ultimately, the arrangements are not impressive.

In contrast, Brandish kicks ass on all fronts.

Tokimeki Memorial Piano Collection (the first one) is excellent, if short.  Very simple arrangements let the original melodies (which are fantastic) shine through.  In my opinion, it's the best piano CD I've ever heard, VGM or otherwise.

What's the verdict on the Okami piano album?

Mediocre. Mostly very slow droning.

I'll second this one.  Absolutely flawless until the annoying vocals in the last song.

Yep, Brandish Piano is already the top of the heap, so stick with what you got.  (it's all downhill from there, unfortunately...)

Another vote for Brandish Piano and a nod to both Genso Suikoden Piano Collections because of Shusei Murai's excellence on the piano and keyboards. The GS ones have touches of jazz among solo performances.

I've always liked the Re-feel Kanon/AIR album.