I used Overwatch for a while in 2vs2 - the point flares have nice synergy if you have multiple ISGs that can cover a lot of map (or just for spotting for your teammates in general). The bombing run is actually pretty potent (keeping in mind you need LOS). Its good on matches that devolve into a stalemate over 1 VP where you can expect big pushes by and against you in one area. It's also pretty good against turtley opponents *cough cough* Cancer Regiment. Other than that you'll mostly use it for the novelty of the Goliath - as Kalli said urban-ish maps that funnel infantry and have lots of cover to cloak in are good for it.
Otherwise you get a lot more bang for your buck if you go for a commander with call-in infantry/ infiltration grenades IMO.
