I'd like to share some first impressions of Colossals performing on the tabletop with the community. I have played with them, played against them. Seen them dominate the game and also being brought down in 1 turn. They definitely are not game breaking, but game changing.
Dealing with them.
Everyone saying that you can ignore them and go for caster kill or scenario win clearly hasn't played against a colossal. Ignoring the biggest thing on the battlefield wouldn't make much sense in a battle, neither does it make in game. You simply can't. With one Colossal toe in the scenario zone or near a flag, you are suddenly one winning condition shorter. Armies who relied on maneuvring and tricks instead of brute force to achieve scenario wins won't cut it anymore. Armies who were able to deliver strong alpha strikes against key models will have trouble as well, since even the best "alpha strikers" usually don't have enough damage output to kill two heavies tucked into one. Colossals offer good protection to the various mechanics, which will certainly show up with them, so anything short of totalling the big guy won't have much effect at all. Good support casters will easily hide behind their big buddies and avoid assassination, so it all comes down to the point where your list needs to be able to kill the Colossal and be quick about it. Oh, no sh.. Sherlock!
Yes, yes Capt. Obvious strikes again, the thing however is, that not all high damage output armies will actually succeed at the task. Mainly those, that rely on infantry to do the damage. With quite a lot of aoe spam coming from the Colossals, single wound infantry really have no options here. This has been obvious since the first spoilers were hitting. Many people welcome the change and a shift away from infantrymachine armies. But what about those that still like their Irusks and Zaals and (insert your faction's infantryswarm caster here) I feel that for several of these casters the changing meta might be a bit too hard to stomach.
To sum it up, in order to avoid accusations of DOOOM! , Colossals fit very well with quite a lot of casters, so they will see regular play, however their impact on the meta might sideline some other casters quite significanlty. Would you guys agree?