The good:
The data is free (provided by an NGO).
It is pretty much up-to-date. It covers lots of countries.
And it also goes back quite some time.
You can download the data in csv or even use their API.
The bad:
Their Tactics, Techniques and Procedures model is inconsistent in that it mixes methods with targets as criteria.
ACLED derives the data from media reports so it reflects their biases.
E.g. in the last years of fight against ISIS, the focus was much more on what the group was doing than what the Iraqi Security Forces did...
...which shows if you compare those years with recent ones, post-2018. It looks like the state forces do today more than in pre-2017 but that is not the case.
Sometimes there is redundancy in the data.
See An Integrated Picture of Conflict by Dunford et al.