Way back in the days of the Dark/Fallen Empires, I had a deck that could turn life into mana for a knockout blow and I also had some mana producing creatures if I lost all my forests. Dark Heart of the Woods was great. In this format, not so much.
I beat Rakdos with the usual Talrand deck shennanigans.
I'd say Dark Heart of the Wood is terrible. In general, if a card does nothing but gain you life, it's bad, and not worth a card slot in your deck. For example, the card Hero's Reunion costs 2 mana and gains you 7 life, without sacrificing anything. I would never play that card in a deck. Dark Heart of the Wood is significantly worse, since not only does it take up a card slot in your deck, but you also need to sacrifice lands for it to do anything. The B/G deck has many, many better options.
Well in Ajani's Deck they are usefull o.O I got myself to 1000 HP and survived waves after waves until the opponent had no more card
+ Online player are not better then AI... lol they are a lot easier as they aren't cheating like the AI. They don't get to ''choose'' their card while playing. The AI does.
In Ajani's deck, yes - but his cards don't just gain life. They also kill your opponent. Gaining life is all well and good, as long as you're advancing your board position at the same time. Dark Heart of the Wood does nothing for your board position, it just delays your death by a turn or two (at best).
On the subject of the AI... yes it cheats, but it also makes terrible plays all the time. A skilled opponent online doesn't cheat, but also doesn't make mistakes. So it's kind a tradeoff. But in general, I'd say a skilled online player is much more of a threat than a cheating yet incompetent AI.
If you really want to gain life, play the Pelakka Wurms.
This is the sh**, last time I played it, my oponent blocked it with pacifism and copied it so every turn he plays, he can put another of that creature xD I was totaly screwed even if I almost won the game, I droped him down to 1 HP and failed for the rest :'(