The drop ships, except maybe the big one with the plasma cannon upgrade, kind of suck after they drop their stuff off. They are good at getting stuff in position but the plasma hoses are not useful at anything really. They can take out light armoured vehicles but honestly what can't?
In the four games we played they only managed to inflict one point of damage on the warstriders. On the wide setting they managed to inflict a very minimum amount of damage on infantry in the open.
If I were the enemy I would probably just ignore them when their stuff was dropped off.
You're right, the desolator would draw an inordinant amount of fire with a commander. Without, it might be a good unit to draw fire while your drop ships moved into position to drop the cargo.
In a skirmish game I would never take one. I'm sure I'll get one eventually because I'm like that.
"The short range on the AA zappers won't keep a determined enemy from getting very close if they want – they could drop (or teleport) at just beyond 9" range and deploy units to just beyond 6" if desired. "
The trouble with that is that if you can get your AA stuff on the drop ship if you are dealing with anyone other than the Shaltari the stuff is pretty much imobile.
In one of the very first games we played we saw a PHR drop ship get shot down and the battle shifted to the other side of the table. The walkers it was transporting survived unharmed but had to move, at 3" a turn, all the way to the other side of the table. Once they got their it was all over.
The Scourge and Shaltari can kill those ships and then get away possibly and moving at 9" vs. 3" or less a turn they are going to really be able to strand ground troops.
For UCM and PHR keeping those birds alive is going to be priority one in a lot of situations, unless they are dropping off stuff to hold an essential objective but as the attacker mobility is absolutely key and even as the defender it will be very important.
Ultimately I think the Scourge will be the best army for new players. They are pretty forgiving with their dropship troop disposition because you can still move around pretty quickly without them. There aren't clever combinations like with the Shaltari that you need to use to be successful.
They are pretty straight forward.
I am very much looking forward to getting enough stuff to play some decent sized games. 500ish points is nice for learning the rules but I bet the game doesn't really come into its own until at least 1000.