I like the set up of your terminator squads, bar one or 2 changes - your sargeants should have something other than a power weapon. anything other than a power weapon. it's the worst choice for them, seriously. and i'd have 1 more THSS in your command squad, preferably on the apothecary.
There's 2 ways I've seen effective deathwing run. The first is Land Raiders. Mount up, beat face. 3 raiders, 3 squads and belial is around 1750 points with upgrades thrown in. this probably requires more lightning claws than you have, though. 1 land raider is a liability in any list because it seals target priority for your opponent. 2 is more desirable, and by then you're commited so you might as well have 3.
The other way is the way I run it, and i'll explain forthwith;
The question is, what are deathwing good at? well, they have some mobile anti light vehicle and anti infantry firepower (cyclones), they are a decent combat unit, graduating to good the more THSS you add. they are fairly survivable, moreso with THSS. the need for chainfists is evident - dreadnought insurance (especially with the amount of av13 dreads running around these days).
What they also are, is slow as piss. They don't have massed firepower (240 points for 2 strength 8 shots), so they struggle with lots of vehicles and lots of hordes. massed low ap fire is also a problem.
One way to deal with the mobility issue is to mount up in land raiders. They other way, is to strip your opponent of his mobility. Against an enemy only as mobile as you, the deathwing terminators match up well against nearly every other army out there. So once you have your core of deathwing, everything else in your army should be set up to provide the firepower needed to get your opponent demeched, having his ap2 templates, plasma etc. out of the game and so on.
So the way I built my deathwing was to look at the options in the codex that were points efficient and allowed me to do that.
Excellent:
- land speeder typhoons with multimeltas. 75 points for 2 s8 shots with a potential for a third? yes please. also add some valuable frag templates.
Very Good:
- predators with autocannon and lascannon sponsons. these are my go to once ive got a decent number of terminators and filled my fast attack with typhoons. they are transport and MC hunters. if these aren't present, their only role is to shake and stun tanks that worry me (demolishers, executioners, vindicators)
- mortis pattern dreadnoughts. also known as the rifleman. Every other marine army has these. They were a dark angels dreadnought first and are available if you have access to Imperial Armour 2. see all the pinch of salt arguments re: use of forgeworld, but no-one should have a problem with these. I only mention them as they're easier to get past your opponent than contemptor dreads (the mortis pattern of which is amazing)
OK:
- ravenwing bikes with meltaguns and multimelta attack bikes. no doubt melta is the pinnacle of anti tank, and yes you get a scout move, but they are often trading a killpoint for a killpoint and the regular meltas might not be in range first turn, leading to them being shot off the table. also compete for slots with typhoons.
- vindicators. S10 ordanance is great. But, the hole can scatter off the hull, they have 1 weapon so are easily silenced with 1 weapon destroyed result and only have a 24 inch range, meaning they'll be put in the line of fire much more often than the predator.
- regular/venerable dreads. there's just better options, i feel. However, multimelta dread in a drop pod is 180 points. 200 for a venerable (which is about what your average marine player pays) and our drop pods don't get shafted by drop pod assault.
- predator w/autocannon/heavy bolter. not as good against transports as autolas, but still decent and has some of the anti horde you lack.
So, it looks like your current list is around 1500 points. At that level, I would consider;
belial
upgraded squad - apothecary, banner, cyclone, couple of THSS.
deathwing squad x3 - cyclone, chainfist, couple of THSS
3x land speeder typhoon w/multimelta
1x predator - autocannon/lascannons.
OR
2x land speeder typhoon w/multimelta
2x predator - autocannon/heavy bolters
If you're not comfortable with predators, the pred can be subbed out for a chaplain or librarian (need to drop a chainfist), to make 3 of your squads a combat threat (one w/belial, command squad, one w/chaplain/libby).
From there, I add a terminator squad because I like 5 troops. Others add 2 more predators, and have been very successful with it.