The Senators can be very good. They absolutely dominated the Rangers last night but ran into an Igor who just said "no", which happens. But all in all it was their best total game of the season. They played very well in a loss to Vegas as well. They've looked better in those two losses in terms of complete hockey games than they have in any of their wins, minus the thumping in Utah.
We know they can be very good. What we don't know if they can be consistently good. They've shown flashes of brilliance in previous years and fizzled out. Not capable of keeping it going.
The changes they made in the offseason addressed some pretty big flaws, and should help to prevent some of the defensive unravelling we've seen in years past, but it still remains to be seen how the core of star forwards can manage consistency.
Time will tell.