Green "stompy" players obviously love this. It's overall much better for Constructed than the Dragon-happy Scaleguard Sentinels. It's especially good with the enchantment Hardened Scales. It can be even better in Modern, as its two green mana symbols are excellent for Green devotion deck. There are creatures like Experiment One and Scavenging Ooze that can gain counters like crazy. It's aggressive enough to be part of a Mono-Green Aggro strategy.
Whatever the case, Avatar of the Resolute is a very strong creature that is extremely Constructed-playable. With its ability to gain tons of counters, Commander decks led by Daghatar the Adamant and Dromoka the Eternal are happy to play it.. It's good in any Green/White deck that runs cards like Cathars' Crusade and/or Doubling Season. Having trample, the Avatar becomes a mighty finisher that can also block flyers with Reach. This is definitely one of the better cards even in a strong set as Dragons of Tarkir.