Maybe a rushdown like Liu Kang or Cage. If you don't want to go that rout you could go with someone like Ermac, where you wouldn't have to switch up your strategy too much, but it would be different enough to be fresh.
Sub-Zero is a rushdown character. He just happens to have one of the best zoning tools to help that rushdown. Which just happens to do an amazing job of keeping out other rushdown characters.
I personally love Sub's combos, because they're straight-forward (wouldn't go as far as braindead) and consistent, but also cool to look at. I don't really care about different combos, because that's just free dmg. It's not like I'm sitting there mashing out my combos saying "Yeah! I've got you now! Try and get out of THIS!" because the other person is just sitting there looking at their meter, waiting for breaker, and once they have it they will very easily get out of it...
Having said that, Sub has plenty of situational combos that you should be mixing it up with. There's:
- Two staples for after 2,2_b+1,2_f+4 xx Freeze.
- The JIP, b+1,2,1 after an opponent is frozen standing.
- The 2,1,2 xx Freeze staples.
- More than one combo for after an opponent is frozen in the air.
- There's all the different XR combos, and you have to know which scale better etc.
- Corner combos, where you have to decide whether to take the dmg or get a Clone out (not a hard decision, but still takes more brain-work than most characters...)
- There's the b+2 reset, and the EX Ground Freeze reset.
- And I'm sure I'm missing some.
Not to mention the fact that often you'll have the opp frozen somewhere away from you, and you may have to adjust your follow-up a little because you won't get there in time for your full staple.
But yeah, I can't imagine being bored with Sub. I love everything about him. His normals, his voice, his costume (and now there's gonna be an unmasked version!), his sword, the way he says "SCOOBIYAH!", his XR (oh man...his XR!). But most of all, I love, no...
ADORE, his wall-rape. When my opponent is running away from me, trying to "zone" me, and I'm just slowly walking forward, blocking each of their attempts, and slowly backing them into the corner before tearing them apart and never letting them back out... Well that's just one of the best feelings in the world, my friend.
Also, his EX Ground Freeze reset nets you 57% in total. You must be doing the wrong one, or not doing the most dmging combos you can be.
Back to his XR quickly: You ever experience it when you have XR, and you're playing against Cyrax, or Mileena, or Kitana, or someone else that throws a lot of projectiles and stuff, and suddenly they're just backing away, trying not to do anything? Not sure about you, but it's an awesome feeling knowing my opponent is scared of me and what I can do, and is having to play outside of their comfort zone and play on my terms. That actually extends way outside of Sub's XR, because that's what his whole gameplan really is.
I don't use any other characters the way I use Sub, and I don't want to. It feels like NRS somehow knew he'd be basically my only character, and made sure to never have him more than one character-slot away. Thank you for that, NRS, and thank you for Sub : )