Should I really be happy about the news? I'm not really sure how to evaluate his writing. The Genophage arc had its moments but also had everything I thought was wrong with the writing of ME3. The resolution of the genophage was absolutely unsatisfying. The formerly morally grey issue became black and white. All the reasons for the genophage were ignored or downplayed (at least with Wrex). Some previously established things have been turned completely upside down. Wrex and Kirrahe didn`t resemble their ME1 counterparts at all. Krogan women were not passive at all in the past, they had an active part in the rebellion as well (see Krogan warlord Shiagur). Not to mention that it is a cheap cop out to set the hope on the females (refusing to bear children? seriously?).
The roleplay experience was also completely unsatisfying. I wish I could give one example where I thought I had control over my character. Doombrows writing is not an example. In my first playthrough I wanted to cure the Genophage, but before that I wanted to confront the Krogan just like I could confront the Salarians multiple times. I wanted to confront him about the Rebellion, about their own guilt for their situation (which they definitely have), get it all out of my system and see what he'd have to say about this. Not a chance. This does not fit in the agenda. So frustrated about this I ended up sabotaging (relodaded and reverted the decision later though). This is a roleplay game, so the character you're playing should be the most important one. Yet for a long time Shepard looks like a supporting actor here who let other people take the lead for him. At least you should be able to voice an opinion, one that is not predefined. The few times you could actually do that, all you got were some uninspired one-liners ("The Krogans weren't ready for a cure bläh :P").
That all being said, I'll keep an open mind about Doombrow. He is also responsible for writing Javik, not only my favourite character, but also the only anti-synthetic who's not a strawman, which is a nice change from the fairy tale villains you usually got. He also wrote some of the best lines. As for the genophage arc, something tells me Weekes had a lot of influence on this, and Doombrow as a relatively new writer followed the senior's lead. This godawful scene with the Dalatrass definitely looks like Weekes' work (and this guy though... please tell me he won't return). Doombrow doesn't seem to be a bad writer per se, but he better realizes that he's writing for a role play game.
Didn't he have a lot to do with the Leviathan DLC as well? I thought that was one of the best DLCs Bioware had done.
Edit: Is that true? I always thought this was mostly Walters` work, because it supports his ending. Anyways, if it is true I'm a little more hopeful. Leviathan DLC was awesome except, yet again, no satisfying roleplay experience. I hardly remember how Overlord was.