While I don't play Reptile, the person I play almost exclusively with (I live with him) has mained Reptile in everything the character has touched. Was he in a comic? He figured out how to main him there, too. So while I'm not the end-all be-all for Reptile knowledge by any stretch, he is the character I am most familiar with fighting by a terrific margin. For context, I play a lot of characters, though I'd probably say my main is Shinnok.
So in my experience, Reptile is simply not a fearsome character. He is a textbook definition of a mediocre character.
Remember, Reptile supporters, that mediocre doesn't mean bad. He is DEPRESSINGLY average. A jack of most trades, and a master of none (with a small exception I will get to momentarily).
He does not excel in the damage department, but that's fine- a nimble, evasive, and mixup sort of character shouldn't be sweating damage. Buffing damage on him is a mistake. It does mean he needs the opponent to make some more mistakes, of course.
His footsies are adequate. Prior to some of his strings becoming plus, I experienced no difficulty just blocking him once and then running pressure for free all day. Most of this time was usually me on a first-day Cassie while he, after a week of solid Reptile practice, struggled to make a dent. Probably a bad matchup, but regardless- for a slithery reptilian guy, his normals are questionably slow.
In regards to his frames, I'm not saying every character NEEDS a safe special or some crazy plus string or some nonsense. As a Shinnok player, it's already easy enough to build silly chunks of meter to spend on block. Reptile, however- would it be too unrealistic to give him SOMETHING neutral or higher that isn't a two-hit string? Even just having a -4 normal swipe (EX has to be unsafe, I don't think there's an argument there) would at least let him try to whiff punish with like f21xxSwipe. He needs meter to do anything and seems to have about the worst time building it in the game.
I'm reminded now of how sloppy his specials seem, all told. His slide is in effect a ghetto Subby slide. That's fine. Elbow dash is now very punishable on block (yay!), but was nerfed startupwise, which strikes me as odd considering what weak rewards it gives.
As a Shinnok player, I cordially invite NRS to give forceballs some kind of purpose so that when I steal that thing it's not hot garbage. It's slower than an iceball and leads to Reptile damage when it hits. Which is never. It's not even a functional meaty mid despite its shape. Obviously its intention is more damaging potential zoning, but at their awful startup, speed, and recovery, Shinnok can teleport and njp punish their use. This does not make for a good fireball. It doesn't make for a good anything. If you want a combo-starting projectile, play Kitana.
Db4 jumping swipe thing is perhaps tied for most crappy special in the game.
Onto the good. I'll save your time, since it's mercifully short. As I said earlier, I do not find Reptile to be remotely threatening. I only play offline, but I think I've lost to Reptiles twice in any extended sets (this does not mean I'm a better player than XYZ Reptile. This is just my experience).
There is, however, one situation that I absolutely hate dealing with and it's oki b2 versus b34. While b34 is barely punishable by some characters, its ability to blow up wakeups versus a combo starting safe overhead makes a really threatening guess. His great d4 allows him to run up and enforce this midscreen on hit. Very cool. If I recall, it was said in this thread Reptile really excels with these tools in the corner. I agree. Man, that guess is stressful. If you keep getting blown up by it, however, that does not implicitly make Reptile great. This particular little situation seems to be one Reptile really wants to lead into, so perhaps allowing him to get to the corner more safely and easily outside of Nimble might be worth a look.
So what would I change about him? Honestly, prerelease seemed fine. I imagine some people at NRS got destroyed by one good Reptile during playtests and thought he was too strong. If not prerelease, I'd personally give him a -4 normal swipe (abort bad whiff punishes since he already had terribly slow normals, build extra safe meter on longer blockstrings) and give forceballs some looking at. Cut startup to make cool new combos for them or cut recovery to make them viable zoning (and make them stoppable at any distance, like what the fuck?). His hitboxes also whiff a lot from what I've seen, which strikes me as unintentional and really stupid.
He's obviously trapped in his almost-identical-variation lot in life, so giving him such sweeping changes isn't going to happen. More universal buffs would be better for him in the long run.
TL;DR Reptile is playable, but not great, which means bottom five is a possibility. He needs meter too much and can't build it. His specials are unsafe and often redundant in their metered use (one drink for each time they start a combo on hit). Forceballs awful for zoning. He has "options", but bizarrely lacks variety.
In NRS gives him damage buffs, I will weep. I only fight the character and I know that solution is simply a mistake.