Battlelords of the 23rd Century - This game is a blast. If your players like traveling to exotic, alien worlds and blowing stuff up, this is THE game. Twilight: 2000 in space.
I haven't played Battlelords since it was with ODC, though I would second it, as well. That said, I wouldn't compare it to Twilight 2000, as that game is known for its brutal
realism where Battlelords is simply known for being
brutal
The ODC Battlelords system was actually
very similar to AD&D mechanically, although it did have some advanced options bolted on (such as armor per hit location). So, if you have experience with AD&D, Battlelords might be an easy transition for you.
Also, thematically, Battlelords has a lot in common with the AD&D 2e "more is better" design mindset — there are dozens of possible PC races and classes in Battlelords, as well as rules for psionics, hundreds of different weapons, armor, ships, and so forth.
Now, if you're looking for something that is actually like Twilight 2000 in terms of plausible far future sci-fi adventure with an emphasis on verisimilitude, you may want to look at 2300 AD (which, despite initially being branded as Traveller, is actually the
official future of the Twilight 2000 setting).