Baron Rivendare's stats were lackluster, he costs a bit too much to play on curve, since usually your turn 4 is dedicated to more powerful drops, and battlecry's in general will always be under your control. There's no way to reliably control Rivendare triggering unless you already have a large amount of board control in which case he is a "win-more" card. But if you don't have board, he gets traded into and never procs his effect and is basically useless.
Brann on the other hand has decent stats, a cheap cost that facilitates being played with other cards and an effect that will only improve as more and more powerful battlecry minions are added into the game. Already with WotOG, we have Ancient Shieldbearer, Twin Emperor Vek'lor and C'Thun that all are augmented to absurd levels by Brann. I can't wait to see what else this guy can do in future expansions. The sky is the limit. We have another year of LoE being in standard so that's 5 more expansions potentially with new cards to get abused.
2
Totally agree with your analysis of Brann... he's definitely one the best designed Legendaries in the game (along with most of the LoE ones, really).
Minor nitpick, but Brann will rotate out of Standard after the first expansion is released in 2017, so we've only got him for another year. Each time Standard changes, cards from two calendar years or before rotate out. This time, it was 2014 (Naxx & GvG), next year all the sets from 2015 go to Wild (BRM, TGT, LoE). So that's two, maybe three more expansions before the Year of the Kraken ends and he's out.
It's kind of sad that the release schedule means that LoE will rotate out so quickly, especially since there are so many great cards in that set (well, barring the ever-present Tunnel Trogg, maybe). But hey... he's sure to be wild in Wild for a long time to come!
15
Just unpacked him and went here to figure out the same thing. I'd dust him, here is my reasoning:
Gruul doesn't do anything when he hits the board, so he's basically a more expensive War Golem... and we know how often that card is used in competitive decks (it's not). Expensive cards like this have to have utterly insane stats or impact the board as soon they're played to be useful. Take a look at The Boogeymonster for another big, expensive, and utterly useless card (it doesn't help that BM has to attack and kill minions to grow, so it's somehow more unplayable than this card).
So, yeah, all that being said, this card is far too slow to see any real play. It probably won't spend more than a turn or two on the board, meaning you'll get 9, maybe 20 damage out of him once or twice. That does sound like a lot in theory, but it will get removed/silenced in competitive games before it gets out of control most of the time.
For 8 mana, you're definitely better playing cards that can immediately impact the board state (Ragnaros the Firelord, Tirion Fordring, Ragnaros, Lightlord, Grommash Hellscream, Al'Akir the Windlord). Look at other 8 mana legendaries like Anomalus, Rhonin, or Chromaggus; even though their effects can be relatively powerful, they rarely see competitive play since they either have no immediate impact, can be silenced, or just have poor stat distribution. And those cards are still arguably better than Gruul (except for the Boogeymonster); late game cards are not about stats, they're about immediate effects.
If you don't have those legendaries/have to play a big card, I would argue that Doomcaller (especially for C'Thun decks), Fossilized Devilsaur, or even Eldrich Horror are better, as they all give more resilient bodies immediately. While the stats on those cards are kind of "meh," they're easier to build a deck around/probably will stay on the board longer. Even if they don't see Constructed play, they're at least decent (not great) for Arena. Even there, the expensive cards should do something when they get on the board to be worth the cost (see: North Sea Kraken, which is actually really good in Arena, yet never sees legitimate Constructed play).
After considering all of this, I'd say that Gruul is pretty bad. Like, slightly better than the Boogeymonster bad. I'd maybe pick him if I was offered him in Arena (there's less silence/removal, more about big stats), but that's really it. There's always gonna be Aggressive decks in Constructed, and Gruul doesn't really fit in any competitive archetype (maybe Astral Communion Druid--but even that deck is really inconsistent/gimmicky).
The game would have to slow down considerably for him to be playable, and even then, there are better options at the 8-mana slot, and below: LordBrontes offers some good insight into the card and mentions below how Edwin VanCleef, a 3 mana card, is much better since he can give a bigger body straight up and allows you to impact the board immediately with other minions/spells.
So yeah, I'd advise dusting Gruul if you want to craft anything else; this is just a straight up bad card, let alone Legendary card.
6
yeah, I'm a little bummed that there's no cool "mutation" animation when he's played, but apparently your opponent still can figure out that the card came from Zerus (the turn history log says "Generated by Shifter Zerus" or something to that effect).