While it is obviously at its most impressive when a ton of mana has been dumped into it (hello, Irencrag Feat), getting a clock going at all is so important that you'll be very grateful to cast it in the first two turns if it means the difference between having a clock or not
Rotom isn't a particularly popular Pokemon, so you shouldn't expect to see this card catapult into the $50 range or anything like that (at least not for several years), but a sub-five-dollar valuation is a bargain
5 mana for a 5 loyalty 'walker is fine
The set with by far the highest average sentiment is Kaladesh , which was consciously designed with an optimistic tone in mind
I'm not satisfied by my counters, there is not a counter that done both Doom Blade and Go for the Throat 's effects except for Death's Approach (who doesn't make me safety) and Murder (who costs too much mana/swamps in early turns): the best things could be something like Abrupt Decay , with black/blue colors