Not an awful card but very overvalued atm. Compared to Master of Evolution you pay 3 extra mana for a 4/5 body with the effect on a single target. To combo this for value you need a mass token summon and to transform at least 3 minions to get value over a master. Requires a board to be a head for value trade and if played in tandem with minions from hand they must have charge or battlecry to gain value from the upgrade. Master just feels way more consistent as it's a good card by itself even when you have no board or are behind assuming you like the same effect. Perhaps evolve is a great 1 of in a swarm deck and for battlecry combos.
Works well with Jeweled Scarab, Abusive Sergeant and Argent Horserider perhaps comboing a massive 3+ minion chain of battle cries. Unfortunately Shaman tends to have poor card draw and wasting an entire card just to buff board advantage cards into an inconsistent upgrade seams like an optimistic strategy at best. This card will be tested with varying results imo but it's far too inconsistent and requires so much set up from a draw lacking class I can't see it overrunning another aggro deck (much like current Face Shaman) or keeping up with greedy C'Thun decks.