Implies that something is so difficult that it can't be done. For something that's just really difficult to do it's better to use 〜にくい or 〜づらい.
Also, the verbs it's used as a pair with are pretty limited. Here are a few more: 賛成しがたい, but 反対しがたい you absolutely can't say. 表現しがたい 考えがたい 動かしがたい事実 受け入れがたい
First example : Lit. "The beauty of the scenery is hard to express completely."
I've noticed that the verbs that tend to use GATAI are pretty scarce so is there a time when this grammar point should be used or can it be used for anything without any problems?
By definition, 難い means "difficult" so that it is associated with things that has problems to begin with.
Would something like 「今夜早く暗くなって道が見難い」be something you say or write (or be quite possibly neither)?
First of all, 見難い is read as minikui here. This is used in conversation and writing. But in writing, 今夜は is better in this sentence. If you meant "something-gagai", we use it in both cases as well but the sentence sounds rather formal in speaking.
Formed from Verb -masu base + gatai Vm - Verb -masu base
想像しがたい 許しがたい 耐えがたい 得がたい 信じがたい 表しがたい
The word pattern "...し難い" can produce many examples.
See also "nikui"?
〜がたい suggests that s.th. is extremely difficult or nearly impossible to do. It is often used with words such as shinjiru (to believe), taeru (to endure),rikaisuru (to understand), eru (to obtain), suteru (to discard), and hanareru (to be seperated from), and refers to mental activity instead of actual deeds. For example, sutegatai implies that one finds it difficult to part with a memory or s.th. one is attached to.