Obviously with the card game, there's not a board or tokens, but is the card game version just as engaging as the board game version? It would be ideal to travel with just the cards, but I'm not sure I want to purchase it if it is severely lacking somehow.
The card game preserves all the same important features present in the board game. All the deductive elements are still present, and the core gameplay is still the same - each player has cards which they reveal as you make accusations.
There are small thematic differences. Instead of the murder in the house, you are on the trail of the murderer. Room, weapon and person are replaced with destination, vehicle and person.
Instead of a board, players each have a destination marker, representing their location. You can move between destinations in order to ask particular questions.
What you are able to do on your turn is dictated by the action card you draw, so there is a little more randomness than in the board game, but also more variety.
Overall, I'd say the card game reworks the mechanics without losing any of the deductive interest of the original.
If you want (a lot) more detail, one good comparison/review is this one on BGG.