February 2005 my husband & I went went on this exact cruise you're looking into, and we had a great time! We too wanted a relaxing, peaceful time, which is why we choose Holland. Yes, they do seem to have a reputation for being geared toward the older crowd, but they're starting to shake this image. And with this newer ship, they've accomplishing it wonderfully. On last year's cruise the diversity of the crowd was younger than on previous ships we'd been on with Holland. They had an Oosterdam "american idol" competition too, which was alot of fun. Let's see if I can answer a few more of your questions.
Extra charges: Shore excursions are extra of course, but most we've done have been worth the money. Alcoholic beverages are extra, as are sodas & speciality coffees. Spas, massage, things along this line, are extra. No open bar on non-alcohol drinks, but they do have soda cards you can buy, at a pretty reasonable price I understand. I can't remember the price because we usually just drank water.
Room service: Yes, anytime you want, and it's no charge. We've only used it one time (unfortunately), and you can order whatever you want. We ordered breakfast, and when it came it was even still hot. There was everything we'd ordered, and plenty of it.
Not sure what you mean by entertainment room/places & other similar???
Dress Attire: We never saw them, but I've heard they really discourage and frown on jeans in the MAIN DINING ROOM during dinner. On this particular cruise, on the formal nights about 1/3 were really dressed up, the rest more relaxed wear, but we never saw jeans.
Breakfast, lunch dinner seating: Breakfast - hmmm room service sounds like a great option for quiet alone time. Also the main dining room serves breakfast, ordered off menu, and is less hectic and quieter. Just tell them you'd like to be seated at a table for two (which we did a couple times), and they'll accommodate. Breakfast is also served in the Lido (buffet style), and you can easily sit by yourself, because there are tables for two. Lunch - same place, same way in the Lido.
Casino slot tournament: Did get into this, but my husband sure enjoyed the roulette wheel, and his winnings ended up paying for all our shore excursions, and a little extra. My game was bingo, which I'd never played before in my life, but I figured, what the heck, why not. I won the first time I played ($140).
Hope this has helped answer some of your questions. Wish I would have found this site before we went on our first cruise; would have really helped getting answers from "real people", instead of the cruise line.
Bottom line - go for it. You'll have a great time! This is a fun ship. My husband & I are going on the sister ship to it (Westerdam) in about a month from now (Eastern Carribean). Ready to go already!