Gene Splicer is an interesting time bomb. It's a Catch 22: damned if you do, damned if you don't. It's both a trap (net damage) and a way to score agenda points given enough inattention from the runner (time bomb).
As a trap it's a bit on the light side. It does 1 net damage per advancement token. Consequently it only triggers when installed, it doesn't help centrals. On the bright side it doesn't cost anything to trigger. Compared to Project Junebug it's 1 net damage per advancement, not 2, which is the difference between a mild setback and a significant setback, given 2 counters. Unlike Snare! there's no 4 activation cost, but no tag either. Also I'd consider Snare! a different kind of trap, more of an R&D/HQ defense since you can't advance it normally to look like an agenda. Psychic Field has the potential to do a lot more damage but is much harder to pull off since it has to be installed and you can't advance it normally. Hokusai Grid only does 1 net damage and costs 2 to activate, but it's more flexible since it's an upgrade that can protect an agenda (nice with Obokata Protocol). Of course you can add a Hokusai Grid to a Gene Splicer server to make it look more like an agenda and add a bit of sting if the runner falls for it.
As a time bomb, a card that the runner must answer Gene Splicer is relatively mild. A Ronin is much more dangerous with the potential to trigger a flatline. Allele Repression is in a way more insidious than Gene Splicer, not providing clear agenda points but allowing the corp to both recur cards and hide agenda's in archives during a run on HQ; not to mention all kinds of tricks when combined with other Jinteki card management tools. Possibly there are more Jinteki time bombs, I just don't know them off the top of my head and time bombs lack a predictable text to search for in Netrunnerdb.
Note that Gene Splicer can also be seen as a straight 3/1 that doesn't give the runner anything when stolen and thus as a way to increase agenda density.
Now to combo's and worthwhile interactions:
- Tennin Institute can add free advancement counters to Gene Splicer. Those can add up to an agenda point and thus encourage the runner to either run more (dangerous) or trash the Gene Splicer (net damage). Of course you can put advancement counters anywhere but with Gene Splicer you can even get an agenda point out of them without Trick of Light.
- Chronos Protocol adds an extra bit of sting by letting you choose which card gets trashed by net damage for the first net damage of the turn. That makes running Gene Splicer a bit less attractive.
- Jinteki: Potential Unleashed also adds a bit of sting by trashing the top card of the runner's stack. Note that unlike Chronos Protocol this happens every time the runner takes 1 or more net damage, not just once per turn.
- Hokusai Grid as mentioned can add an extra net damage (for 2) and make the server look more like an agenda server.
- Trick of Light can be used to move some advancement counters to an actual agenda, e.g. to fast advance a Braintrust or a Philotic Entanglement.
And here's a combo that looks interesting, until closer inspection:
- Tori Hanzō has a double effect in a Gene Splicer server. She turns one net damage into brain damage if the runner runs (at an effective cost of 5) and facedown she makes the server look more like an agenda server. Unfortunately you have to reveal her before the runner chooses which card to access first so she'll get trashed before she can upgrade that net damage from Gene Splicer.
Somewhat out of the box Gene Splicer might see some play in Weyland because when scored it counts as an agenda and thus can be forfeited to power e.g. Archer or Jemison. It can also be liquidated with Back Channels (a trick that's also useful in Jinteki btw).