The two games are kind of similar genre, so I think it makes sense to compare them. Both require the player switch weapons fairly often.
In Mutant Alien Assault, most of the weapons with the longest reload times have a sound effect that plays when the weapon is available to fire again. For grenade, rocket launcher and mines, it’s pretty obvious, a solid click or beep. The sound for the sniper rifle is a little quieter and easy to miss. The plasma ball (not 100% certain what to call it?) weapon is the one weapon with a long reload time where I can’t hear anything to indicate it’s ready to fire again.
In Super Crate Box, there are a lot of weapons, like the mines, the rocket and grenade launcher that have long reload times but no indication that I can see or hear that the weapon is ready again. I think this has made it a little more frustrating for me to use these weapons, when I don’t have the small sound reinforcing the reload time.
Small thing, but one of those design questions it’s worth considering. If you have something that always takes a certain amount of time, are you doing anything visually or audibly to show that to the player, or are you assuming they will memorize it?