My partner wants to buy me a mechanical watch, where should I start?

Skeleton as a first mechanical is fine if you genuinely like the look. Just know you're paying for decoration as much as movement quality at that price. Nothing wrong with that, but don't expect a beautifully finished in-house calibre

Honestly at $500-800 I'd look at a Seiko 5 or a Hamilton Khaki first.Get used to owning a mechanical, then go skeleton later. But that's just me being boring.

Skeleton watches under a grand are mostly Chinese movements in shiny cases. Some are decent (Seagull, some Orient), but a lot are junk with mineral crystal and no real finishing. If you want skeleton, look at Orient Star or maybe a used Tissot T-Complication. Otherwise, +1 on the Hamilton.

Wait, Tissot T-Complication is way over budget new. Used maybe. But yeah, skeleton at this price is a gamble.

I bought a skeleton watch as my first mechanical and I love it. It's a Seagull M182SK. Cost me about $300. Is it as nice as a $3000 watch? No. But I stare at it all the time and it makes me happy. If you want skeleton, get skeleton.

That's fair. Happiness is a valid metric. I just get annoyed when people buy skeleton watches expecting Grand Seiko finishing for $400.

Practical stuff: check the crystal (sapphire preferred), check the movement (Miyota 8N24 is a common skeleton base, it's okay), and check the size. A lot of skeleton watches ate 42mm+ and wear huge. If you have small wrists, look for 38-40mm. Also, skeleton dials can be hard to read. That's the tradeoff.

Good point on legibility. I had a skeleton once and gave up trying to tell the time in dim light. Pretty, though.

Also consider whether you want an exhibition caseback instead. You get to see the movement without sacrificing the dial. Best of both worlds for a first mechanical.