This year uefa champions league round of 16 is not tough, the only tough matches in the round of 16 are Barcelona vs Napoli and Atletico Madrid vs Inter Milan.
I don't think i'd agree with that, i think every match in the CL knockout stages is tough, of course there are going to be teams that are stronger and are favorites to win, but it always doesn't mean it would happen in that way, there would prolly be one or two upsets and even if there is none, the underdog teams can make the game tough and more interesting (even if they end up losing). The competition gets tougher and more interesting as it progresses, but even the RO16 can produce some cracking games.
If you go through the fixtures of the uefa champions league round of 16 you will see that most matches there are not tough, we already know the clubs that will be knocked out in the round of 16. It will be hard for an upset to happen because those big clubs will want to score so many goals against the weak clubs to make the second tie easier.