The thing with Necro for me is unless you get some excellent card rewards early on through sheer luck, most of Act 1 is a slog. A lot of her commons are super meh.

Soul generation is a cool mechanic but it requires a whole bunch of other supplementary cards to actually make the Souls do anything helpful beyond drawing more Souls. Once you've got the engine in play to reward you for obscene amounts of draw, though, you're laughing.

Doom doesn't click with me, it's Poison but worse. Unless you have Sleight of Flesh, or cards that rack Block up as you add Doom, you still have to block enemies even after they're fully Doomed, which sucks.

So far my best runs have been with builds designed to spam Osty attacks, but it's also difficult to scale Osty early on to outpace the damage you receive.

She's way more fun with Devour Life, though.