TL;DR: In appearance, Neanderthals may look very different from "us", whoever "us" refers to, but then we look very different to each other.
Imagine in the pre-television era, the thoughts of a south-east-Asian peasant encountering Gerard Depardieu: "What is this strange, hulking creature?"
I suspect if we met a Neanderthal, we would not think him the most odd looking person we saw that month.
In terms of reproduction, Neanderthals could certainly breed with modern H. Sapiens, but it's not clear to what extent the offspring would be fertile. I suspect they would do just fine, but this is not actually known.
There is no bright line delimiting what differences between groups constitute them as two species, versus two subspecies.
Generally if two groups are incapable of mating and producing viable offspring, they are clearly separate species, but there is a considerable range of possibilities between species which cannot interbreed, and subspecies which are visibly different, and perhaps rarely interact, but are capable of interbreeding freely if the occasion arises.
For example, lions and tigers can interbreed and the offspring are generally fertile, though the second generation is often of delicate health. However they generally do not interbreed because their ranges do not overlap, and their habitat and lifestyle are different. So this is an example where the speciation process is almost complete.
The notion of "what is a species" is politicised, because the concept is used in conservation law. Therefore there are powerful incentives to classify two groups as separate species or as mere subspecies, in order to give an endangered group the protection of the law, or to deny it to them as a mere subspecies. These powerful social forces make it difficult to come up with any objective definition of the distinction between "species" and "subspecies".
It's not really known where in this range falls the distinction between Neanderthals and Homo Erectus.
- They are possibly simply a racial group, capable of interbreeding freely, producing offspring with a combination of characteristics from the parents.
- But it's also possible they are more akin to the Lion/Tiger example above, where interbreeding is possible, but the offspring are not necessarily particularly successful.
- If the offspring are partially fertile, then a female hybrid is likely to be more successful in reproducing than a male, based on Haldane's rule: https://en.wikipedia.org/wiki/Haldane%27s_rule
For comparison, Coyotes and Wolves (and domestic dogs) diverged over twice as long ago as Cro-Magnon Man and Neanderthal Man, and they interbreed just fine. So it seems likely to me that reanimated Neanderthals would have no difficulty interbreeding with modern humans.