Venser, the Sojourner is my favorite card, because it speaks to me from multiple angles.
First and foremost, I love blink effects. Something as small as a blink can change the way a lot of things operate, by repeating enter-the-battlefield triggers, rescuing your mind-controlled or perpetually-tapped creature or other permanent, or even just giving something pseudo-vigilance. Or, perhaps in a cube, you can do something nasty like blink a wincon and proceed with a wrath - or even nastier, an Upheaval - and continue onward uncontested. It's a lot of versatility, making Venser's first ability elegant, even though it's incredibly simple.
Venser's second ability is perhaps a bit confusing to a control deck trying to abuse his +2 with the likes of Wall of Omens or Mulldrifter; why would you ever use this ability? I always believed this is because Venser was designed for the BantPod deck when it was standard legal, a midrange monstrosity that abused etb triggers and eventually amassing a huge board. With Venser, you can build up advantages until you can simply overwhelm your opponent; a -1 with "Creatures are unblockable this turn" could just as well read "win the game" in the right deck. I enjoy cube, and find Venser doesn't need to use this ability to be good, but having the option allows him to fit in more decks than many other planeswalkers who don't have as straightforward abilities as "Draw a bunch of Cards". For this reason I think he trumps most other guys outside the Lorwyn 5. Both the +2 and -1 can work together, but they don't need to.
Venser's ultimate is incredibly powerful - a little wonky, to be sure, but powerful. Spells giving you free, colorless exiles is exceptionally good, and cantrips like Preordain suddenly become incredibly valuable. If you have a Batterskull on the table, you're in amazing shape. And this isn't an ultimate that takes forever to get to, either.
Venser is far from the best card, or even best planeswalker in MTG. But, all three of his abilities are potentially powerful, which lead to enjoyable experiences every time I play it. Because Venser's abilities require a little bit of planning, I find that deck construction with him becomes quite interesting; some already good cards gain additional value, some strategies suddenly have an entirely new angle when he hits the field. Being able to think ahead and see real benefits of that planning make playing the card a very rewarding experience.
I'm still playing krasis though
I know cards like Luminarch Ascension have been wincons for decks like this in the past, although I've never seen anybody express interest in something like that for cube. "Cards that work after you've kind-of already won the game" is not a category I value too highly in this format.
Nevertheless, I appreciate seeing these interactions just naturally come up with cards we already want to run. I especially like stories about interactions I didn't previously consider, so I will keep my eye out for more.
I might be overreaching here, but I haven't explored this particular combo space in a while and I wonder if there are other new ways you can use this kind of self-bounce for other locks. The One Ring hardly needs support IMO, but maybe there can be a really fun package to assemble for some drafters?
While it's true that Bonecrusher Giant has a smoother play sequence, going from adventure to creature, I'm not totally off of this. If it's your only turn 2, it's your 2-drop. If you have alternatives, play the alternatives. If it's still in your hand while you have a board presence, you can just find ways to get value off the burn and another creature later. If you've got 5 mana, it does a mediocre FTK impersonation.
Basically I love adventure cards because they allow for several different lines of play, which allows a little more flexibility with how you use your mana. I really don't know that it has the raw power to hold its own weight, but I just really like the design and will consider testing it out.
I think UW or UB control decks will appreciate it if you can find room, but I'd also think it's a low priority card. I think I'd likewise sooner add Lorien Revealed.
Yeah, I wanted to hedge myself by saying my list, since we don't do initiative / monarch (I should have indicated that explicitly). I would certainly need to re-assess if we used those mechanics, since the value of aggression goes up - I'd put a lot more trust in your experience there.
Edge cases definitely, and I don't know they make up for the narrowness, but I think it's a cool card and fun to think about.
I think wheels are pretty popular. Often times the good ones are cost prohibitive to people who are stubborn about proxying (e.g. Me) but I think when they're available and the list has a couple combos floating around, people are likely to include at least a couple.