I don't really find reddit comparable to forums, mainly because reddit is also built around recent comments. It has very rudimentary search functionality, and the way submissions and comments are scored discourages long conversations. Unless you're on a really small subreddit, stuff falls off the first page quickly, and your comment will be far less visible if posted half a day later. This is completely different than forums, which optimize for conversations that last for several days to a couple of weeks, sometimes much longer.