Honestly no where near enough time at Alwick Castle another hour at least would be better. In addition to the time, despite the tour stating that entrance to the castle and gardens was not included we were basically held hostage on the bus while the driver went and purchased tickets for all of the people on the bus. We had purchased ours in advance but weren't allowed to get off the bus until the driver returned with everyone else's tickets.
I had a good trip to Lindisfarne and Alwick Castle. I was somewhat disappointed at Lindisfarne. Our stay there lasted for a little more than an hour, which is far too little. It's a place for contemplation, but there was no time for that. The highlight of the tour was obviously - according to the bus driver - Alnwick Castle. Alnwick Castle was very nice, but two hours would have been enough, not three. Lindisfarne would have been a better experience with one of those hours added. All in all it was a good trip though with a friendly bus driver, who provided us with information on the way to island and castle.
This trip was great, however there are things that could have been better. You have to take into account the weather for one thing, and the tides. I would recommend booking when you know what the weather is going to be and after checking the tide times for Lindisfarne. It is also 2.5 hours to Alnwick, and 2.5 hours back, which really cuts into the time you have at each stop.
You also need to keep in mind that Alnwick Castle entrance fee is not included in the price of the tour. This is something they really should advertise before buying. Also, if you're not a big fan of Harry Potter, you may get overwhelmed by all the brooms and wizards flying around.
Overall, it was a fun experience and I would do it over again.