It's a pretty unique hybrid genre game, you don't really get a lot of first person + RTS experiences, I think that's the big enduring appeal. It also gives you a lot of vehicle types to pick from, which became Pandemic's signature game style as seen later in Mercenaries and Star Wars Battlefront.

Part of the appeal of being a hybrid genre game is that there just aren't really many of them, because after the 90s games kinda settled into some pretty well-defined genres. You have 3rd person action games, FPS, RTS, RPGs, etc, all pretty cleanly delineated, and they all start getting judged based on those genres conventions.