I love this series! 9/10
Okay, so it's certainly not perfect - most of the plot is driven by MacGuffin artefacts (the Scrolls of Thebes, the Puzzle of Horus, the Medallion of the Medjai etc) and its run-time of barely twenty minutes per episode doesn't allow for the level of depth and development that some of the characters are crying out for. However, as an action-based fantasy cartoon series, I feel that it has a whole lot going for it.
The characters and the voice work are very well done. Alex is a fantastic hero and protagonist, and I think the fact that the series becomes more and more the story of his journey is absolutely the right direction for it to take. Chris Marquette gives an extremely engaging, charismatic and sensitive performance, and his changing voice perfectly mirrors the emotional and physical development of Alex as a character.
John Schneider also does an excellent job as Rick, giving the character a pleasing Indiana Jones vibe. Grey DeLisle and Tom Kenny may not provide the best English accents ever, but their performances are always on-point. I do like what Jim Cummings does with Imhotep, although I think it's a shame that he doesn't get very much chance to engage in appropriate banter with the good guys.
The locations and guest characters are always well conceived and well used. My particular favourites are Yanit and Fadil, whose continuing relationship with Alex is the most interesting unexplored aspect of the series in my opinion.

A strong and enticing opening 8/10
This is a very good start to the series that sets up an overriding plot that is both sustainable and enticingly weaved into the established "The Mummy" universe, or at least into a new but appropriately familiar version of it. It introduces and establishes the main characters and their interplay very well, and also stands up as an adventure in itself.