We are a group of ex Tabletop gamers which are looking for a fun board game which goes in this direction (but we do not have the same time as before. Mainly nostalgia ). It should be more or less one game. Some expansions are ok, but not buying specific heros or monsters or card decks. The most important point is: As little downtime as possible for the not active players (at least after some games, when the flow is good).
We watched reviews for:
Super Dungeon Explore
All the reviews sounded amazing (so we would be happy with a broad range of systems), but not really touch on the downtime aspect. With ca. 4 guys we do not want to wait for 20min. before we can make the next decision or dice throw. At least you should be able to plan some stuff, which is impossible if your turn depends to much on the last guy.
SpaceHulk is pretty cool for two players, but starts to become slow with 4 players. Especially compared to the rather simple rules.
I hope this is more or less clear.
I can definitely recommend Mage Knight. Amazing game. It's rather long (playing time), though. I have only played it in a cooperative way, where planning ahead is perfectly doable (so not much downtime). In a competitive setting, I think you would need to know a bit more from what your opponents did, so the downtime would be higher.
Castle Ravenloft (and the other D&D board games) could be worth a look.
And you could also take a look at Dungeon Command or Earth Reborn (these are mainly two-player games, though).
Professor, isn't it time for your nap?
There's not really too much downtime in Descent: Journeys in the Dark (Second Edition), unless you're playing a five-player game as the Overlord. The hero turns can seem to last forever, especially while they're scheming and plotting where exactly to go. Even so, the downtime is pretty minimal. It's a great game.
I would also suggest the D&D Adventure Games: Ravenloft, Ashardalon, and Drizzt. These games are strictly co-op with no Overlord or Dungeon Master. It's just you vs. the game. The downtime in this is also pretty minimal.
I would love to suggest Claustrophobia, but it's only for two players.
Mice and Mystics