I think while somewhat gimmicky, the genestealer cult has some great combinations. I mentioned in the Tyranid tactics thread the possibility of doing a sling shot with units like ravenors or shrikes turn one. Deploying in your own zone they have permission to charge turn one, (usually can't reach) The patriarch (and other two
ICs) can infiltrate and still have permission to assault turn one. By daisy chaining them all together, it is likely that you can get a pretty powerful force into your opponent turn one. The trick is you have to build the army around and supporting that idea. Super weakness if you are going second, or have the initiative stolen.
'We will have to wait for the cult codex (and possibly new nid codex) to find out if things like if a venemthrope/malanthrope shrouding bubble effects the cult. (Currently it only effects those with the Tyranid faction, not those with genestealer cult faction.)
When basing off the genestealer cult, I think the goal is all about speed. Shrikes and Ravenors can get across the board fastest, while malanthropes help a couple of heavy anti-vehicle hitters get across as well. Mini las cannons and the stone wreckers should have some success against vehicles, while the massed rending attacks everywhere should eat any troop concentrations. No
AA to speak of, but even knights would have to fear the massed rending and the two big ugglies. Once again, going second or having the initiative stolen can really wreck your day, and that makes the army more of a gimmick deal.
Genestealer cult based
1850
This I think would have a little more success potentially against all comers. When going first the stealth/shrouded infiltrating and potentially assaulting broodkin can wreak havoc on a gunline or disrupt whatever the opponent is planning. While 600 points is quite an investment, if you are devastating your opponents plans from deployment on, then you are controlling the game. Big creatures and choppy things popping in from reserves (mostly on turn 2) are now arriving just as spore field is striking and while embroiled in close combat with the cult, they potentially don't have the time or weapons available to redirect on the drop in army.
I think it's more survivable for
TAC because if you are going second, or facing null deploy, you can outflank the entire cult and drop in the other guys, while leaving the spore field on the table infiltrated into the safest positions. It's very difficult to wipe out the entire spore field turn one, and none of them count for scoring needs. (This often does put you behind the eight ball where it comes to maelstroms.)
Surprise NIDS
1850