Unlike the HQ section, which was basically reworked from the ground up, the Troops portion of the new Tau codex is more a matter of subtle changes. That's not necessarily a bad thing. Tau Troops might not be Grey Hunters or Guard blob-squads, but they were solid choices stuck with slightly out of date points costs. And thankfully, those costs are now more in-line with the game-wide standard.
Fire Warriors are pretty much unchanged; they dropped a point in cost, and got free photon grenades, a slightly dubious gift. They can still trade their pulse rifles for carbines, which nobody is likely to jump for given that carbines trade one extra shot in a 3" band for losing a full foot of utility, and their EMP grenades got a point cheaper as well. The upgrade to a shas'ui is not especially tempting, particularly since it's unchanged cost has become relatively more expensive given the reduced cost of Fire Warriors, and the markerlight and target lock is pretty steep; all told, that single BS3 markerlight will cost 34 points. Given the changes to the Fast Attack slot, which we'll get to soon enough, that's unlikely to be worthwhile in the majority of cases.
The basic troop choice of the Tau Empire, Fire Warrior squads are solid, especially if they're backed up by an Ethereal or Fireblade. They have arguably the best standard weapon in the game, and unarguably the best standard anti-infantry weapon. Unfortunately, despite an initially-promising allowance, Games Workshop has FAQ'ed against letting them take missile drones, leaving them once more with no access to special weapons. Given the 'combined arms' nature of the Tau, it doesn't really come as a surprise that you need to make multiple sections of the army work in tandem to accomplish their objectives. It's still a bit of a disappointment, though.
If the Fire Warriors were basically just tweaked slightly, however, the Kroot were given a more wide-ranging, though very subtle, alteration. While their points have remained basically the same, they traded a now-standard 6+ save for a point of S, and a second attack from their Kroot rifles. At first glance, this looks like the Kroot got worse, and as far as their role as counter-assault unit goes, they probably did. More importantly, however, for just one point per model Kroot can now have sniper rounds; that's right, 7 point 24" sniper rifles, that can benefit from markerlights. They can also bring their hounds along, giving the Infiltrating (and therefore Outflank-able) Kroot Acute Senses, or Krootox riders, though 25 points for a S7 AP4 rapidfire weapon is a bit steep given the prevalence of that particular S/AP combo in this book. The Shaper is still around as well, and has even gone down in cost by nearly a third, though since all he's good for now is a one-point LD bump he's of questionable necessity. Not a bad upgrade, per se, but if he challenges anything tougher than a naked Guard or Eldar sergeant he's dead, and he brings no useful shooting or support abilities.
It's tough to say categorically whether Kroot got better or worse, because what they really got is different. The inclusion of sniper rounds provides impressive value for points, given the steady increase in MCs and T5 units with high cover saves the latest round of codexes has been offering. While battlesuits and tanks provide access to high strength, low AP shooting, it's often on elite, expensive platforms; there is no Tau equivalent to Tac squads with melta/missile, or Guard HWTs. The new Kroot, however, might be able to fill the role of taking on the toughest models in the game, not with the best weapons, but with sheer weight of fire. Combined with Outflank/Acute Senses, and the fact that they can switch from their standard rounds to their sniper rounds at will, the new Kroot are a fast-moving torrent of fire, ready to force saves until something drops dead.
Oh, also, there's the Devilfish I guess. The basic vehicle hasn't changed, but alterations in the Vehicle Battle Systems have made it worse. You might have already noticed how I feel about this hunk of junk.