Ant,
The original voice for Cate was a hired actress, as is the new voice. That's no big deal--the fact that Armstrong was different, and VASTLY inferior at that, combined with the change in the style of the game's writing, shows the team had some major personnel changes. And none were for the better.
An add-on a year after a game came out is NOT unusual. OFP:Resistance came out 1 year almost to the day after the original release. Well, in Europe anyway. It took another 3 months before it came out here with the first 2 patches integrated. GR:Island Thunder was a year after release.
Here's NOLF2's big failure--it didn't improve upon the original or even try to match it. The original had Bruno, the head of UNITY and Mr Smith, Mr Suave Annoying, Ms Fat Opera Singer, Volkov, the Baron and Baroness, and Armstrong. The sequel had Armstrong in a weak supporting role, UNITY head off somewhere, no equivalent to Smith, Mr Annoying as voice-only tapes, Volkov in a weak supporting role, the HARM Director, the Mime King, and a boring Japanese girl as "arch nemesis"--yawn--with the character of a dried noodle.
Only the HARM Director was decent. The Mime King was "eh." Original, yes, but only eh. The Japanese girl was the biggest mistake. A straight role!?!?! Did NOT belong in the game. Put her in Deus Ex 2 or AvP3 or something, not NOLF.
The overheard guard conversations in the sequel pale to the first one's. Even the guards themselves. I couldn't stop laughing in the original the first time I opened fire and heard a bad guy shout, "Oh oh, bullets!" and run for cover!
The high-point of the original NOLF was the Armstrong/Fat Pig and Armstrong/Cate interactions. The latter fall flat in the sequel and there's no equivalent to the former.
The Jedi Master
PS Screw it, I'm gonna reload NOLF1 again and replay it. I've realized just how much I loved that game!