We found out the hard way...that not all travel agents are equal. Especially if you are a first time cruiser...take Kuki's advice and find a 'cruise travel specialist'.
Most Cruise Specialist are not only familiar with the the different cruise lines but have personally been on most of the ships! This is valuable information when choosing a cabin, knowing personally what the food and ambience of the ship is like. They'll also have the experience if you need to make changes or hit a small snag.
Of course everyone is different and what appeals to one person might not to another, BUT a Cruise Specialist will try to find a cruise line that match the passengers for a nice fit.
(e.g. older passengers might not enjoy a Disney cruise no matter how beautiful the ship..but might love HAL or Celebrity.)
IF we've never been to an area/country before we always book 'shore excursions' through the cruise lines. Might be a little more expensive but we know we'll get where we're going with little or no hassle and back again before the ship leaves, (nothing worst than standing on the dock seeing your ship fade in the distance...this happen to friends of ours) and it gives us a nice over all view of the local area. Then when we return...if we feel comfortable, we book our own excursions.
There will always be, 'coulda, woulda' shoulda, but that's part of the fun and experience. You'll LOVE cruising!!!