Shall I pick a character for you? [ynq]
If you were never asked to pick a race and class in any roguelike, you probably haven't played a lot of them. This approach allowing for different playing styles is present in many games, and the subject of regular criticism. For example, it has been pointed out (by Andrew Doull) that vertically partitioning player abilities across classes is often a waste of mechanics. The advantages and disadvantages of class-based systems are much-discussed and I don't really feel the need to restate what others have said on this subject. Instead, I'd like to focus on race/class combinations here.
Firstly, how are races differentiated from each other? Many roguelike games do this by giving their races affinities for different combat abilities. Dungeon Crawl Stone Soup, for example, features so-called aptitudes for various melee weapons, spellcasting schools, ranged combat etc. Nethack gives them different stat spreads.
This leads to a more or less predictable effect: Some combinations have higher chances for winning than others. Players often describe the easiest combinations as "beginner strategies", implying that they are overpowered or just not challenging/interesting enough for a more seasoned player. Unfortunately, it also often leads to the existence of very underpowered combinations. Why would anyone ever want to play a troll wizard if trolls have an abysmally low magic stat? Why would you choose to play a race/class combination in which your race is reducing the capabilities of your class? Only if there was something else that made them attractive. Both in Crawl and Nethack, there are additional racial features that may alleviate racial penalties. For most of these underpowered combinations, this doesn't really result in any additional survivability. Consequently. Crawl explicitly marks them as not recommended, and Nethack even removes some combinations entirely. In-universe this might make sense. Your game might be set in a fantasy universe where elves are feeble and dwarves are stupid. Thus, you might want to forbid the existence of elf fighters, or dwarf mages, or whatever. However, from a gameplay point of view, there's a lot of gameplay potential that's just plain wasted.
What if races had something to offer for all classes? Take the example of ToME4. The dwarves, the race with the highest magic penalty in the game, are a popular choice for archmages precisely because of their high constitution and saves. ToME4 defines races not just via stat bonuses and penalties, but also via their racial talent trees. Another example highlighting this is the Shalore race: These elves have the highest magic bonus in the game, make excellent archmages. But ironically, Shaloren Berserkers used to be very powerful because of one of their racial talents, and despite their strength penalty.
I think this approach has some merit. Imagine a race/class model, where all combinations are equally playable. Where the choice of your race does not limit your choice of class, and vice versa. Of course, there could still be beginner options and expert options, but they would be this by design. I haven't really seen a roguelike game that implements such a model (ToME4 has or at least used to have its own problems with classes themselves having balance issues) and my own experiments are immature enough to not be a good proof of concept.