I take it you don't like the hedge of holly or boxwood bushes, but to me they seem to just be getting to the look that was probably intended when they were planted -- that is, joined. They're at an awkward moment now, kind of like train cars! But so close.. I'd be patient to get the grand hedge they were meant to be. As for cutting back the lilac, I favor letting it grow as well. After seeing lilacs in their glorious full size at the New York Botanical Garden's beautiful lilac garden, I can never truly love lilacs in the inevitable pruned iterations we usually see them in residential gardens. So you've asked for what to change and I've said nothing with what you have. Just nurture and add to it, especially to conceal the clutter that's now visible.

Most lilacs will survive hacking to the ground, so you can prune them pretty severely. To renew them, the recommendations are cutting back a third at a time. Most people prune after blooming as if you prune in the fall, you'll lose a year's blooms.

I'm not a fan of those yew (are they yew?) balls fencing in the lilacs, but you appear to have some garbage cans you're hiding with them, so keep them if they are hiding unsightly stuff. I'd leave them at the end of the driveway, unless you had better plans for that space.