Best explosions i've seen are in Rainbow Six 3: Raven Shield , and those are made with a high number of small sprites combined with debries .A nice thing is that the smoke remains in the air for some time beore it disappears ,very realistic . When simulating a detonation ,too much fire is bad , you need to have a blast ,something violent ,less fire more smoke and debries,adding a shaking effect to the camera is also nice,also make it loud :D