It's great news. In my personal view he really shook up what was inevitably becoming a bright but very insular trio who'd been together for so long, because he was full of new ideas - the kind of character maybe who reminded them of themselves when they were younger and hungrier - and I think they loved the sense that he was making them all think in a fresher way. Especially Klopp. So I think his return is excellent. It's interesting that he's yet to be given an actual title and role, but, unless Buvac comes back like Nigel Tufnel at the end of Spinal Tap, I'd assume that Pep will in practice if not in official title take his place.
I think as I said a while ago, the only down side to this is that it will minimise the time he can spend doing what he was truly innovative doing, which was working on bespoke training sessions with senior players to improve certain skills, and bringing on the best of the Academy players and integrating them into the first team squad (Trent, for example, has loads to thank him for). Tactically he's a truly brilliant micro-manager. But doubtless he can pass on his ideas to other coaches and build up those links again by delegating.
The really good thing is that, unlike so many assistants we've seen arrive after a trusted confidante has gone, he really is liked by Klopp,and he's a great source for new ideas.