Is this sentence correct?

I'd turn it into two sentences. The first is fairly straight forward. (Changes in bold.)

Maybe next time it should have covered less features more deeply, but that's only my opinion.

The second part is a bit trickier but what you're saying is that those who attended had their questions answered.

In any event those who attended had their questions answered satisfactorily.

Having said that you've not said that the attendees actually asked questions, but they might have had unspoken questions which the presentation covered. In that case I would say.

Despite that the presentation was broad enough to cover any questions the attendees might have asked.

I'd say:

Maybe next time we should cover less features, but more in-depth. Still, it seems that attendees' questions were answered adequately.

(No need to state or apologize that this is your opinion. That's implied)

Tony this might not answer ur q, but

"Maybe next time he/she should cover fewer features more deeply; and that's only my opinion; but judging from other attendees' questions it was OK."

Keeping it as a sole sentence:

"Maybe next time should covered less features more deeply but that's only my opinion and checking the attendees questions it was OK."

"Maybe next time should covered less features more deeply but that's only my opinion and reviewing the attendees questions it was OK."

""Maybe next time should covered less features more deeply but that's only my opinion and hell with what the attendees questions were about."

"Maybe next time [it? the...? we...? etc] should [have ?] covered less [fewer?]features more deeply [, ? ; ?] but that's only my [my? my?] opinion [--? ;?] and [while?] checking the attendees [..s' ?] questions it [the response? your answer?, etc] was OK."