You're going to encounter a decent amount of Japanese is almost every single PC-FX game, so if the thought of this at all gives you pause, I'd say the console isn't worth it for you. That is to say, there are too few games where Japanese isn't a factor.
That said, I'm not at all fluent in Japanese (I can only identify a handful of characters - just enough to decipher menus and simple names and places) and I absolutely love the system. Even if you know zero Japanese, if you're willing to deal with a slight learning curve, you'll be able to get something out of the console.
For these people:
Der Langrisser FX (a sequel to the game "Warsong" on the Genesis and TurboGrafx-16/PCE) is an absolute must if you liked the original or strategic RPGs. JP language stuff might be an issue for you in this one, for the menus mostly.
Yuna FX is a relatively short digital comic with a lot of character, and a bunch of fun unlockable, replayable mini games.
Boundary Gate is a first-rate first-person dungeon crawler RPG. JP language stuff might be an issue for you in this one.
Last Imperial Prince is a sidescrolling action RPG set in a gorgeous world with a unique battle system.
Team Innocent is more than "playable," it's great fun. It's a Resident Evil-type game that drops flat paper-like anime chicks into a 3D environment. This game will make you wish the PC-FX controller had an analog stick. JP language stuff might be an issue for you in this one.
Dragon Knight IV is another good entry in an epic series. This one combines traditional overhead RPG gameplay with strategic battles and scantily clad girls to impress. The game is not hentai, make no mistake. JP language stuff might be an issue for you in this one in understanding the story.
Ruruli Ra Rura is a f*cking WEIRD platformer. It's worth recommending not because it's great, but because you'll never play anything like it.
Shanghai: The Great Wall is one of the best entries in the Shanghai tile-matching series that you can find on just about any console. If you like Shanghai games (I do), this one's a must-own.
Everyone else will recommend the regular Zenki, Bubble Bobb.... er, Chip Can Kick, and Zeroigars so I won't worry about mentioning those.
I ought to go back to my initial point, though; if the thought of a little Japanese at all turns you off, don't bother with the system. I can't tell you the number of people I've seen buy a PC-FX, get a bunch of games and then sell it off 1 or 2 months later. These things probably have the highest turnover rate of any console in history. If I was smart, I'd already be starting a betting pool on how long it'll be before you sell yours.