Just want to chime in reiterating everyone's thoughts already here that this language is fun, interesting, and worth your time investment to investigate.
The biggest hurdles I had coming from OO Ruby were 1) how to handle state, since you no longer can just hang information off any arbitrary object attributes, 2) pattern matching (but now that I grok it, I love it, it's so useful and leads to more concise code), 3) lack of inheritance (although oddly, I don't seem to miss it, it just leads to a somewhat different code design), 4) OTP semantics (which after you mount the learning curve, make a lot of sense from a resiliency standpoint).
There are a number of neat little details not yet mentioned or emphasized here such as full Unicode support, full-fledged macros that give you full AST access (in a non-homoiconic language, that is a rarity!), custom sigils (http://elixir-lang.org/getting-started/sigils.html), the ability to easily call into any Erlang library, the fantastic :observer.start() utility for visually observing tons of details about a running pid hierarchy, etc.
One possible hurdle unique to languages that feature message passing between independent processes (pids or process id's) as a core feature is that once you have a pid hierarchy, it seems to me that inevitably, one of them will get a backlog of messages requiring you to either apply back-pressure techniques (slowing down upstream synchronous messaging by slowing down replies, basically) or pursue some other strategy (code refactoring etc.) when messages start to get discarded under load due to overflowing the pid inbox.