same writer, same illustrator. that should be enough to give a try.
both main characters have supernatural abilities. there are mysteries about the past.
the differense is the main character of Ability, is more like frankenstein than Rai. in fact, there's still no character in ability similar to main character of Noblesse.
Ability is yet new so it still has not gotten as strong as Noblesse, but it's strong point is that it's more realistic (so far). and i think it's the most similar Manhwa to Noblesse.
The writer and illustrator are the same in each series, which will likely be enough of a reason for fans of Noblesse to give Ability a shot.
Both series feature supernaturally powered characters with a hint of mystery and intrigue over their past. Ability is really early in it's run, but it seems more action focused, and lacking in the great comedy that Noblese has. You could also accuse it of being a little too slow, and maybe missing a brilliant plot hook to keep the reader interested, although it appears to be getting a bit better recently.
That said, Ability is worth a read, just don't expect it to come roaring out of the blocks. And on the off chance you haven't read Noblesse, then definitely give that one a try, it's a seriously good read.
Both are done by the same manhwaga (Korean mangaka you can say) and even characters from both look very similar to eachother, such as Un (Ability) and Reigis (Noblesse). Both are also fairly slow paced at the beginning, as it provides a little REALISTIC character devlopment (the main character in Ability doesn't immediately become OP strong within the first set of chapters, it takes time realitically) so if you don't mind that and actually prefer it, your good to go. Also both have very interesting stories, especially Noblesse where it indeed takes a while to find out all the details of the MC's (Rai's) past, which is actually a good thing since it gives time for character development (and there are quite a lot of characters_ and then later provides flashbacks. Either way, if you like either one there is a very low possibility you won't like the other.
Same author and artist.
Both series start off at very slow pace and develop from there onwards. Both have supernatural elements them in them. While Noblesse features MC who is strong as hell, ABility features relatively weak MC, but strong enough to survive in the cruel world which awaits him.
IF you liked one, you will enjoy other :)