en.wikipedia.org/wiki/Category:Grammatical_categories is a helpful superset of the possible dimensions and some of their possible values. The dimensions that I would consider applicable to verbs:
- agent person + number + gender
- object (whether there was one, and possibly person + number + gender)
There is overlapping functionality, eg passive voice and reflexity ie object, and impossible combinations, eg aspect is not necessarily distinguished in all tenses.
And of course, what some languages express with verbs, other languages express with nouns or adverbs or even random particles.
You could also look at verb arguments, ie valency.