I got the Drell Adept yesterday (and Asari Adept the day before) and I'm just loving them. I had enough practice with the Asari Adept, so the Drell Adept was new to me. I followed the guide to leveling him that someone posted here, and it seems to work really well for me. Pull + Reave is an awesome biotic combo.
The thing is, I was playing on bronze, and even then, I felt a little squishy. Unshielded enemies were no problem for me, but what should I do for shielded/armoured opponent? Someone said reave + grenade, but cluster grenades are so damn finicky when I toss them.
Regardless, I like the Drell Adept much more than the Drell Vanguard.
The Drell Adept is squishy no matter what... that's why I emphasized never engaging close. If they close on you, RUN... use your mobility to find a better angle. On Silver/Gold it's obviously always better to stick with your team, but there will inevitably be those moments when you'll need to separate due to circumstance.
And to those pooh-poohing grenades... DON'T. Grenades, just like any game with them, are a precious commodity but when used in the proper circumstances are LIFESAVERS.
For all grenade using classes out there, remember this (I haven't seen this explicitly posted yet) : Your grenades respawn
independent of your character... they spawn *specifically* to that ammo box. Yes, even on Silver and Gold. You can even see the grenade if that particular ammo box has it available... and also see when it doesn't. So if you're in an emergency and the ammo box near you is out, break out and hit the next one... you can restock back up to 3 in short order if you know the maps and the ammo box locations.
Back to the Drell Adept... why do I think this class is top tier and has the slightest of edges against the Asari Adept (especially with the Stasis cooldown increase)? Because of Cluster Grenade. This grenade is (arguably) better than Inferno's, Proximity, Sticky, Frag, etc. Why? Because you can increase the shrapnel count... meaning that even without getting a radius bonus, you still hit in a wide radius due to more shrapnel leaving your hand. Also, with increased shrapnel count, if you want to get fancy, you can aim for a corner or wall and have the shrapnel bounce in different directions. Or aim at the feet of a Banshee/Brute/Atlas and tag it will ALL your shrapnel. With proper cycling like I detailed before, you can throw 1.5-2 grenades per round and have at least 2 at the start of the next round... that's if you use one ammo box. On smaller maps like the white map from the demo, you can throw upwards of 4-5 per round and still have 2 at the start of the next round. On this map, I typically can hold the entire lower room by myself (with teammates at the top vantage point) against Brutes/Ravagers/pretty much everything (except Banshees in a group) with the squishy Drell Adept because of those Cluster Grenades and proper ammo cycling (and ensuring that no enemies spawn behind me on the middle level).
Sorry for the mini-rant, but remember, grenades are your FRIENDS in this game... don't ignore them.