Regarding openness, I felt that NOLF2 was a bit more open than NOLF1. The difference was minimal, though. As for the choice of mission weapons
Ab, it did annoy me as well that it disappeared.out stealth and shooting, like everything else it's affected by the value of your 'RPG' stats, which didn't exist in NOLF1. Personally, I thought that the game lost a bit with the introduction of the RPG system. First there was the problem you've mentioned, and second it made intelligence gathering about point collecting which, to me, didn't fit the game at all. I still finished the ninja level stealthily, though.
Bottom line is I didn't like it at much as NOLF1. However, it still has great characters, great set pieces, it's still very funny, and it still catches the sixties spy thing. Also, I really loved the engine at the time, I loved Cate's new design, and it has a few things that added to the NOLF1 experience like the kicking over objects thing, or the possibility of unscrewing light bulbs. And it's still better than Half Life.