I like that idea! The first portal you encounter could be treated as a tutorial and could take several attempts to properly open. For example, the first time the portal almost opens, but fizzles out. The second time, it opens and soon closes. then, the third time, it opens but it's size fluctuates and the edges wobble (in 2.5D i'm assuming the portals would be seen as ovals and not just 'lines' like in AO and AE if you know what I mean).
Abe could also show some physical reaction, like when the portal abruptly closes he is knocked down by whatever force or energy he is tapping into, like when he is zapped by a chant suppressor- maybe with a zap of that crackly electric portal stuff for good measure
