Resale issues are there, but it lacks many popular apps, which are expected to arrive on Windows 10 mobile soon. So you have to be patient about apps availability now. This is main issue.
Other than that, they are great and run very very smooth, even their cheapest models.
I have experienced Lumia 430, 532, 540, 640 (non XL) and they are excellent in terms performance and even gaming.
430 and 532 have no flash light (hell annoying). Lumia 640 (non XL) is the one i liked most, though it has not impressive selfie camera.
They even have manual shutter speed controls that help a lot in photography, if used properly.