Wow. I've seen the intelligent-raccoon crowd take over threads before, but this one really takes the cake.
You're absolutely right of course, the lack of our genus isn't magically going to make sea otter civilizations. That's not how evolution works. By far the closest critters to sentience are still the australopithicenes. If anyone is going to build civilizations a few million years down the road it's them. But, again, that's not really the point, eh?
Moving on. Without full sentience and within-a-lifetime tool invention, the australopiths aren't going to have near the same impact that we did. Still, big brains, bipedal legs, and hands are all powerful advantages. We could expect the hominids to continue steadily expanding out of Africa - first into the Middle East and Southern Europe, then quickly along the Indian Ocean basin, and gradually north into Europe proper, the Caucasus, and (probably) central and eastern Asia.
Unlike Homo, which tended to quickly become a keystone species and then kill off its local relatives (how Europe and the Middle East became Neanderthal habitat and southern Asia went Erectus before Sapiens swamped them both) the Australopiths will alter ecosystems without becoming the center of them. Social hominids are decent competitors for tight resources, and given 2.5 million years it's likely that fire use (not necessarily making) will be added to their repertoire. Species in direct competition - bears, other primates, some canines and pigs - will be gradually outcompeted. In dry regions you'd see a decline in megafauna that could be spooked away from watering holes. Meanwhile the average size of the big critters will decline across the board. Still, this is all less than in OTL.
Without hitting the sapient wall (as we did ~100,000 years ago) it's unlikely that you'll get hominid "monocultures." By which I mean that any relatively diverse ecosystem is likely to end up sporting 2-3 different species of intelligent, bipedal primates. Speciation will be along diet lines - big-jawed herbivores, long-fingered fishers and trappers, small-game hunters with long running legs, smaller-bodied scavengers (Homo may have started off here, OTL), etc. In cold regions, epicanthic folds and wide cheekbones will replace prominent noses and facial hair. In very dry ones you'll get species with big fatty deposits on the rump for storing water (the San were already heading this direction in OTL after only a couple hundred thousand years in the Kalahari; leave hominids there for a million years....). In fringe environments in the Congo Basin you'll get a short-limbed, vaguely pygmy-looking variety that will compete with Chimps, but only gradually make inroads into their habitat.
Australia and Siberia may avoid hominid colonization entirely, and the Americas certainly will. That means a lot more megafauna outside of Australia, where the drying trend was the biggest factor. Even there I'd expect another size level up in the herbivores and the survival of a smaller variant of the marsupial "big cats."
If intelligence does eventually arrive, half a million or so years down the road, it will be rather depressing how many species get swamped by the winners. They're also going to have a rough time getting civilized. Most of the species in Europe and Asia will have had as much as a million years of evolving side-by-side with early hominids. Just like the African wildlife of OTL. That means the mammals are going to be nigh-on impossible to domesticate. The ones that we tamed in OTL will mostly be on the slow die-out circa 2008 TTL, because the same factors that make them easy to catch and tame make them easy to catch and eat.