Having only played with nomads for the first time yesterday, I'll hope you all forgive my relative ignorance of what may be already covered ground as far as balance discussions are concerned, but these are the things which I would tweak having gleaned some initial impressions.
T1 AA/arty; I'd nerf its aa damage by 2 dps to bring it to 18 dps. This would make it closer to other t1 aa in terms of anti air effectiveness per unit, and means that the extra mass per unit that you're paying largely goes to the artillery ability.
On top of this I would reduce cost of the unit by 2 mass, and build time by 10, so that the nerf on dps doesn't mean that its use as aa only isn't too expensive and time consuming when compared to other factions aa units. This still leaves it as slightly less effective as an aa piece, but I see this as a necessary price for the extra arty ability.
For comparison, other aa costs 28 mass, build time 140, and does 16 dps vs air, the nomad one would cost 34 mass, build time 170 and do 18 dps vs air if the changes above were implemented.
T2 Goliath; I like the idea of this unit as a 't2 lab', although I don't think it has the power to compete with other units on the battlefield. Labs at t1 don't see use after a couple of minutes into the game, as they are simply ineffective against anything except engineers, and if this balancing is carried to this unit, I fear it wouldn't see any use at all.
My solution would be to increase the projectile damage from 110 to 150, so that it can kill any t1 tank in two shots. As it stands, 3 t1 tanks can beat it (excluding any micro), with the t1 costing less. By making it a 2 shot kill on t1 rather than a 3 shot kill, it becomes effective as a mobile t2 rush to beat t1, while remaining vulnerable to other t2 units thanks to its low range and health. It would still remain however a raiding unit, as engagements with large groups of t1 would still be ineffective.
T2 aa; I think its broadly comparable to other factions, though I would slightly increase its damage radius from 3 to 3.5, as other t2 aa has damage radius 4. I think this is probably needed, despite its slightly higher projectile speed, as it does have about 10% less damage than other t2 mobile aa.
The unit I think needs nerfing at t2 is the mobile missile defense, as per unit mass its currently much more effective than stationary pieces (though I concede this is disregarding associated costs to each like t2 fac+engies, or t2 upgrade on com).
I'd suggest that 1 projectile every 3.5 seconds would be more reasonable than 1 projectile every 2 seconds.
T3 Tank; As it stands, I don't think the t3 tank is in any way cost effective against other t3. it has less total dps, and less health per unit mass than other factions units. As a standalone balance, I would suggest swapping the ranges on its weapons, so that it has 200 dps at 35 range and an extra 120 dps at 25 range rather than the other way around. The solution however (I beleieve) needs to be done joint with the beamer assault tank. Imo at the moment, the nomads have no really effective unit compared to other factions between its t1 tanks and its ultra heavy tank.
Its t2 main tank costs more than comparable units because its amphibious, and the t3 tank needs a buff as described above, while the beamer I think at the moment is rubbish.
Take the Beamer vs bricks for example.
Coming in at a cost of just over 9 bricks, the only advantage the beamer has is that it is slightly quicker. Apart from that it has less range, the damage of only about 5 bricks (though I acknowledge it won't suffer from the same kind of dps drop off as the bricks in an encounter), and less health than 3 bricks.
An individual solution to the beamers problem would I beleive be to increase its range to 35 (or slightly higher), increase movement to 3.5, and drop the cost to around 9000 mass (from over 11000!).
Coming back to the point of a joint solution however, instead of the changes to the t3 tank and the beamer detailed above, perhaps the t3 tanks cost and power be cut to put it in the range of titans and loyalists, while increasing the damage and health of the beamer (leaving the mass unchanged), so it becomes a heavier more expensive equivalent to bricks and percies.
Finally, the experimental heavy tank and the missile tank both (imho) need a nerf, the missile tank especially. I like the idea of the missile tank, but it is simply too strong for its cost at the moment. I've not really thought of a neat solution yet, but maybe I'll have more ideas soon.
Well thats me finished thinking about balance, and I think this is the point for me to say that overall I think its is looking amazing and I can't wait to see it finished, I hope I haven't sounded too critical because the vast majority of land units I think are well balanced, and where I've made suggestions I think of it as fine tuning.
Also a disclaimer- the suggestions I've made, while being picked up as issues in game, are based almost entirely on the accuracy of the units db for the nomads, and I'm well aware that as a beta that it is in the process of balancing an so some things I've quoted may not be entirely correct.
More to come on air and navy I hope, feel free to disagree and sorry this post was so long
