If you feel that something has both positive and negative aspects then you have ambivalent feelings about it.
Having mixed feelings or contradictory ideas about something or someone:
some loved her, some hated her, few were ambivalent about her
an ambivalent attitude to Europe
To say that councillors are ambivalent about the idea is an understatement.
Those sentiments are a far cry from her early years when she had an altogether more ambivalent attitude towards her singing.
In practice, we have managed to do better than our ambivalent attitudes suggest.
If something is open to more than one interpretation then the adjective equivocal is more appropriate.
Open to more than one interpretation; ambiguous:
- However, the evidence on industrial disputes is at least equivocal and there are indications of higher levels of conflict that challenge notions of quiescent workforces unwilling to take action.
If something is partly good and partly bad then it is a "double-edged sword"; it "cuts both ways".
Macmillan: Partly good and partly bad
It might be simplest to just say that the thing has "both good and bad aspects". Then you can go on to talk in detail about what they are and what's good/bad about them.