If you have the time to get caught up on a several thousand pages long multimedia web epic, read you some. It's got time shenanigans and truckloads of universe building, though it starts out kinda slow, since true to the CYOA format, it was originally reader command driven. It's one of the biggest (both in fanbase and in sheer length due to creator Andrew Hussie's absurd update rate which, even with two gigantic update pauses of several months, still averages something like three pages a day) webcomics on the internet and between the constant use of .gifs, flash, and even later on some HTML4 shenanigans makes it one of the only truly WEBcomics, not just 'comics that are hosted on the internet'. Definitely has the best soundtrack of any webcomic.
If you don't have time for all of that, try its ancestor, Problem Sleuth. Entirely driven by reader commands, also takes advantages of .gif panels frequently, and involves three hardboiled detectives in a crazy-ass CYOA which rather than time shenanigans mostly involves spacial abstract crazy-awesomeness and quantum states. If you like all the potential world-bending stuff you can do with Oblivious you'll love this.
And inspired by Homestuck, what started out as a subcomic on their forums became its own comic, Prequel, set in the universe of Elder Scrolls: Oblivion about a week before the actual game. Its subtitle, "Making a Cat Cry: The Adventure" is apt, because Katia Managan, recovering alcoholic and Khajit of questionable repute, cannot catch a break. It's an emotional rollercoaster, and oh my god do I want to jump halfway into it and just show off the HTML wizardry the comic engages in, it is SO COOL, but spoilers.
Monster Pulse is an AMAZING deconstruction of the kids-with-monsters, digimon/pokemon type scenario, taken more realistically and seriously with some of the best written teenage/older kid characters you're going to find.
Monsterkind (similar name but very different story) is about... well it's still in the world build phase, but basically it's about a world where half the population is generically referred to as 'monsters' in a vaguely Jim Henson-esque way, but are treated as second class citizens and relegated to districts increasingly segregated and gentrified by the ratio of how many of them are human and non-human. But it's not nearly as depressing as that concept makes it sound.
And for something non-serial, Awkward Zombie. Pop culture comics mostly related to video games. Very funny.