Scourge of Armagon has some fun maps, though they're sometimes marred with annoying deathtraps. The new content (weapons & enemies) are mostly superfluous. There are a couple new power-ups, but their usefulness varies wildly. For example, one power-up will summon a random enemy to help you out. The catch of course is that you're chances of getting something cool like a Shambler are nil. Most of the time, you'll just end up with a dog. Still, it's a mostly entertaining romp that doesn't wear out its welcome.
Dissolution of Eternity is a bit more robust. While there are a few of the standard sci-fi bases & medieval ruins, this expansion also takes place in other worlds. Don't be surprised to visit element-themed realms, a monster-infested Egyptian maze, and so on. New enemy types are also interspersed here and there, but again, nothing as standout as the original Quake. Instead of new weapons, you can now pick up lava nails & multi-rockets. Naturally, they're more powerful and have the bonus effect of not replacing the standard nails & rockets. To put it another way, you get A LOT more ammo. In a short time, you'll be cruising through this expansion and laying waste to everything in sight. IMO It's not nearly as balanced or as intricately-crafted as Quake, but it's still good fun.
